gfapi: handle graph switch (cwd, fds, locks)

- Migrate open fds to new graph
- Migrate locks held in open fd to new fd
- Refresh CWD, so resolution of relative paths happens on refreshed
  inode (on new graph).

Change-Id: I4b18083b9b290107ebda1f917fc85b635ab72fb4
BUG: 953694
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/5059
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Raghavendra G <raghavendra@gluster.com>