Fix: sessiond: leak of application context in channel

Fix: sessiond: leak of application context in channel

Issue observed
--------------

ASAN generates the following report when the session daemon exists after
running the tests/regression/tools/context/test_ust.py test suite.

  lttng-sessiond: ==930543==ERROR: LeakSanitizer: detected memory leaks
  lttng-sessiond: Direct leak of 8 byte(s) in 1 object(s) allocated from:
  lttng-sessiond:      0 0x7f8d1706c33a in __interceptor_strdup /usr/src/debug/gcc/gcc/libsanitizer/asan/asan_interceptors.cpp:454
  lttng-sessiond:      1 0x55e36fa6d107 in alloc_ust_app_ctx /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/ust-app.cpp:1368
  lttng-sessiond:      2 0x55e36fa82f73 in create_ust_app_channel_context /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/ust-app.cpp:2912
  lttng-sessiond:      3 0x55e36fa9eeac in ust_app_channel_create /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/ust-app.cpp:5062
  lttng-sessiond:      4 0x55e36faa9fef in find_or_create_ust_app_channel /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/ust-app.cpp:5936
  lttng-sessiond:      5 0x55e36faab610 in ust_app_synchronize_all_channels /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/ust-app.cpp:6147
  lttng-sessiond:      6 0x55e36faac12e in ust_app_synchronize /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/ust-app.cpp:6208
  lttng-sessiond:      7 0x55e36faacc29 in ust_app_global_update(ltt_ust_session*, ust_app*) /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/ust-app.cpp:6268
  lttng-sessiond:      8 0x55e36faa910e in ust_app_start_trace_all(ltt_ust_session*) /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/ust-app.cpp:5850
  lttng-sessiond:      9 0x55e36f920343 in cmd_start_trace(ltt_session*) /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/cmd.cpp:2826
  lttng-sessiond:      10 0x55e36f9ffac5 in process_client_msg /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/client.cpp:1779
  lttng-sessiond:      11 0x55e36fa077c0 in thread_manage_clients /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/client.cpp:2588
  lttng-sessiond:      12 0x55e36f9e4d85 in launch_thread /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/thread.cpp:67
  lttng-sessiond:      13 0x7f8d15c9d44a  (/usr/lib/libc.so.6+0x8744a) (BuildId: 2f005a79cd1a8e385972f5a102f16adba414d75e)
  lttng-sessiond: Direct leak of 5 byte(s) in 1 object(s) allocated from:
  lttng-sessiond:      0 0x7f8d1706c33a in __interceptor_strdup /usr/src/debug/gcc/gcc/libsanitizer/asan/asan_interceptors.cpp:454
  lttng-sessiond:      1 0x55e36fa6d059 in alloc_ust_app_ctx /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/ust-app.cpp:1367
  lttng-sessiond:      2 0x55e36fa82f73 in create_ust_app_channel_context /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/ust-app.cpp:2912
  lttng-sessiond:      3 0x55e36fa9eeac in ust_app_channel_create /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/ust-app.cpp:5062
  lttng-sessiond:      4 0x55e36faa9fef in find_or_create_ust_app_channel /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/ust-app.cpp:5936
  lttng-sessiond:      5 0x55e36faab610 in ust_app_synchronize_all_channels /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/ust-app.cpp:6147
  lttng-sessiond:      6 0x55e36faac12e in ust_app_synchronize /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/ust-app.cpp:6208
  lttng-sessiond:      7 0x55e36faacc29 in ust_app_global_update(ltt_ust_session*, ust_app*) /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/ust-app.cpp:6268
  lttng-sessiond:      8 0x55e36faa910e in ust_app_start_trace_all(ltt_ust_session*) /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/ust-app.cpp:5850
  lttng-sessiond:      9 0x55e36f920343 in cmd_start_trace(ltt_session*) /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/cmd.cpp:2826
  lttng-sessiond:      10 0x55e36f9ffac5 in process_client_msg /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/client.cpp:1779
  lttng-sessiond:      11 0x55e36fa077c0 in thread_manage_clients /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/client.cpp:2588
  lttng-sessiond:      12 0x55e36f9e4d85 in launch_thread /home/jgalar/EfficiOS/src/lttng-tools/src/bin/lttng-sessiond/thread.cpp:67
  lttng-sessiond:      13 0x7f8d15c9d44a  (/usr/lib/libc.so.6+0x8744a) (BuildId: 2f005a79cd1a8e385972f5a102f16adba414d75e)
  lttng-sessiond: SUMMARY: AddressSanitizer: 13 byte(s) leaked in 2 allocation(s).

Cause
-----

In the case of application contexts, alloc_ust_app_ctx() copies the
provider and application context names. However, these fields are not
free'd by delete_ust_app_ctx().

Solution
--------

The application context and provider names are free'd during
delete_ust_app_ctx() when the context type is LTTNG_UST_ABI_CONTEXT_APP.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I0759018ec1811cf6246b5a80d4f5a7545c63910a