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
Fix schema format in template generation unit tests

Change-Id: I0c13d972100596e33e3f439e97326144a7fabbb4
Avoid error on double-delete of nested stack

When deleting a stack that has a nested stack previously deleted, the
process fails because the nested stack cannot be retrieved from the
database.
To solve the bug, the nested stack is now retrieved from the database
ignoring the deleted stacks before the deletion process begins. Then
a NotFound exception is raised, and then when it's catched the nested
stack will be ignored.

Change-Id: Ib863527dbfb0200b833a4e90b5a4fd50f469c1ce
Closes-Bug: #1261436
Merge "Avoid error on double-delete of nested stack"
Merge "Fix schema format in template generation unit tests"
Merge "Validate number of instance metadata entries"
Merge "Improve tools/uninstall-heat"