mount/fuse: save the basefd flags in the new fd

Upon graph switch, the basefd's flags were not saved in the new fd created
for the new graph upon which all the further requests for the open file
would come. Thus posix was treating the fd as a read-only fd and was
denying the write on the fds.

Change-Id: I781b62b376a85d1a938c091559270c3f242f1a2a
BUG: 998352
Signed-off-by: Raghavendra Bhat <raghavendra@redhat.com>
Reviewed-on: http://review.gluster.org/5601
Reviewed-by: Amar Tumballi <amarts@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>