doc/man: lttng(1) command pages: always include `common-footer.txt`

The end of an lttng(1) command manual page source now looks like this:

    include::common-lttng-cmd-help-options.txt[]

    include::common-lttng-cmd-after-options.txt[]

    include::common-footer.txt[]

`common-lttng-cmd-after-options.txt` contains the "EXIT STATUS",
"ENVIRONMENT", and "FILES" sections.

`common-footer.txt` begins with the "RESOURCES" section.

This will make it possible to insert an "EXAMPLES" section between
`common-lttng-cmd-after-options.txt` and `common-footer.txt`.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I1eee42d7386f4671d9825e9d3e131e54f868ee39