libglusterfs: Explicitly open /dev/stderr logfile

From: Bharata B Rao <bharata@linux.vnet.ibm.com>

Currently if stderr is specified as logfile, /dev/stderr isn't opened but
stderr is directly used. However libgfapi closes the logfile (and hence
stderr) from glfs_fini() which results in stderr becoming unavailable for
the application that links to libgfapi. Prevent this unexpected behaviour
for the application by explicitly opening /dev/stderr like it is done for
any other logfile.

Change-Id: I76b754598a2acf40b91ff0461726c5918e278c84
BUG: 1038924
Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Reviewed-on: http://review.gluster.org/6477
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>