As part of a CVE keystone has started checking[1] the timestamp
of signed ec2 token with default TTL of 15 mins. We can't
store the ec2 url anymore for future use for those.
This moves the caching logic to BaseWaitConditionHandle class.
Conflicts:
heat/engine/resources/signal_responder.py
heat/tests/test_signal.py
[1] https://review.opendev.org/#/c/724124/
Change-Id: I6b74faed820caccd39210bd48a212b2dedca46b9
Task: 39985
Related-Bug: #1872737
(cherry picked from commit 3047ca7d36)
95296e55c6