By waiting to add resources to our lists until after the last
operation that can fail, we don't have to remove them from their lists
in the error path.  Also, we should hold the idr mutex until we know
whether resource creation has succeed or failed, to avoid someone
finding a resource in our table before we're ready.

Loosely based on work by Robert Walsh <rjwalsh@pathscale.com>.
Signed-off-by: Roland Dreier <rolandd@cisco.com>