ceph: EIO all operations after forced umount

This patch makes try_get_cap_refs() and __do_request() check
if the file system was forced umount, and return -EIO if it was.
This patch also adds a helper function to drops dirty caps and
wakes up blocking operation.

Signed-off-by: Yan, Zheng <zyan@redhat.com>

diff --cc fs/ceph/addr.c
Simple merge

diff --cc fs/ceph/caps.c
Simple merge

diff --cc fs/ceph/mds_client.c
Simple merge

diff --cc fs/ceph/mds_client.h
Simple merge

diff --cc fs/ceph/super.c
Simple merge