Make os-quota-class-sets test not break quotas

Ib0cde08dfaa0f6a5e180d247864fb59d76eca903 added a test for nova's
os-quota-class-sets API. To test if the default quota is successfully
changed by bumping all quotas with a by a value of 1, and adding locks
around all quota specific API tests to prevent race conditions.

If the quota is unlimited, -1, then the test sets the quota to 0
(-1+1), causing any concurrent attempt to boot an instance (by a
parallel test) to raise the error 'FixedIpLimitExceeded'.

To address the first issue, +100 instead of +1 to the current quotas.
This addresses the immediate gate issue by preventing us from hitting
any quota limits.

Because this is an admin only test, we expect that the blueprint to
run without admin will just skip this in the production cloud case.

Co-Authored-By: Joe Gordon <joe.gordon0@gmail.com>

Change-Id: I7660037eee2e5b04e5dd1dfa779d15cb361cc939