Both NODE and NODE_RES locks were acquired opportunistically if so
requested by the user. LUInstanceCreate requires, however, that the
actually locked elements on NODE and NODE_RES level are the same.

This patch changes the locking of NODE_RES such that those locks are not
acquired opportunistically any more. Instead, the mandatory locks are
set to the acquired NODE locks once they are actually granted.

This fixes issue 622.

Signed-off-by: Thomas Thrainer <thomasth@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>