client: add inode on IMPORT
client: add inode on IMPORT

If we get an IMPORT and don't have the inode, add it.  This fixes a race
like:

 mds0 -> client .. mknod reply (or similar)
 mds0 -> mds1 .. migrate cap
 mds1 -> client .. send IMPORT
 client <- mds1 .. rx IMPORT, but don't have inode
 client <- mds0 .. rx mknod reply, add it.

With this fix, we add the inode and set up the cap on IMPORT, and when we
get the mknod reply we update the inode immutable fields that aren't
present in the cap message (rdev, symlink target).

Fixes: #1513
Signed-off-by: Sage Weil <6dd34506bbd5e58221bbb3e4732d97c91f02277b@newdream.net>

ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph