fsal-proxy: implement the status() of FSAL API

Now is_open() depends on the status() API to get open flags, so we need a
proper pxy_status().  Otherwise, cache_inode_rdwr_plus() will loop forever as
the default status() returns FSAL_O_CLOSED.

Signed-off-by: Ming Chen <mchen@cs.stonybrook.edu>
(cherry picked from commit 1a0cb0c5827c967d91c99df8c5ecf1e37fef335a)
Signed-off-by: Soumya Koduri <skoduri@redhat.com>