Improve tools/uninstall-heat

Inform users that the script doesn't remove related role/user from keystone.

Change-Id: Ia0a7cb37ae568e37c86ff9047361c42186c21ab4
Validate number of instance metadata entries

The Server resource arbitrarily limits instance metadata to five
entries, when the actual provider's maxServerMeta limit could be much
higher.  Make the Server resource check the provider's maxServerMeta
absolute limit and enforce that limit in validate().

Change-Id: Ic00fc6f3a41ae783e43bd7f2df8663263d9cbf90
Closes-Bug: #1260427
Merge "Validate number of instance metadata entries"
Merge "Improve tools/uninstall-heat"