gfapi: Closed the logfile fd and initialize to NULL in glfs_fini

Currently if logfile is closed and other threads call gf_log
after glfs_fini() is executed, it may lead to memory corruption.
Adding gf_log_fini() which closes the logfile and initializes
the logfile to NULL, thus any further logging happens to stderr.
Also added gf_log_globals_fini() which should be filled in the
future to release all the logging resources.

Change-Id: I879163e1a3636e65300d166f782517ee773cab65
BUG: 1030228
Signed-off-by: Poornima G <pgurusid@redhat.com>
Reviewed-on: http://review.gluster.org/6552
Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>
Reviewed-by: Shyamsundar Ranganathan <srangana@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>