gfs2: Prevent inode creation race

When a request to evict an inode comes in over the network, we are
trying to grab an inode reference via the iopen glock's gl_object
pointer.  There is a very small probability that by the time such a
request comes in, inode creation hasn't completed and the I_NEW flag is
still set.  To deal with that, wait for the inode and then check if
inode creation was successful.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>