Fix double free in label monitor

Fix double free in label monitor

The pointer passed to initialize_inotify() is already managed by a unique_ptr.
In case of initialize_inotify() failure the pointer was being passed to
security_manager_app_labels_monitor_finish() where it was wrapped in a
unique_ptr again.

Add a helper non-throwing function operating on raw app_labels_monitor pointer
for properly closing it. Use it in security_manager_app_labels_monitor_finish()
and security_manager_app_labels_monitor_init().

Change-Id: I6f3b5883fde53ba3ded7764f3121f59ace053a10