api, glusterfsd: Cleanup upon failure in glusterfs_ctx_defaults_init()

This got introduced due to 656711d935000c16. Coverity
also picked this up as CIDs 1256176, 1256178, 1256180.

Signed-off-by: Vijay Bellur <vbellur@redhat.com>
Change-Id: If12fa0075634383975846181917a2f9650f790e3
BUG: 789278
Reviewed-on: http://review.gluster.org/9213
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Reviewed-by: Shyamsundar Ranganathan <srangana@redhat.com>