Update default rate limits for nova

Update limits to current limits in
nova/api/openstack/compute/limits.py.
Remove sentence that dos not apply anymore.
Remove unneeded colspan elements, they're the same everywhere.

Fix reference to make this build after changs in api-site:
it's now #serverMetadataKey

Change-Id: Ib225533aaba9ad4250ebefe0707b87f2ea8dcb66
Closes-Bug: #1299907