Initialize liblttng-ust-common in dependent libraries

liblttng-ust-common is a new public library introduced in this
developement cycle to contain the shared state between liblttng-ust and
our other libs that can't link directly on liblttng-ust. The constructor
of each of these libraries should now call the liblttng-ust-common
constructor early in their own constructors to ensure proper execution
order.

  * Rename library constructors with the _ctor suffix to help
    distinguish them from other _init functions.
  * Hide the fd-tracker init fonction, the liblttng-ust-common ctor
    should be called instead.
  * All libraries linked on 'liblttng-ust-common' call its constructor
    early in theirs.

Change-Id: I8e083f392b4ef2427addd00120cffc61a6314697
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>