gluster: Move glfs_close() to create's clean-up

glfs_close() is a classical clean-up operation, as can be seen by the
fact that it is executed even if the truncation before it failed.
Also, moving it to clean-up makes it more clear that if it fails, we do
not want it to overwrite the current ret value if that signifies an
error already.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>