This updates a warning string and the release notes for the
IRONICCLIENT_CACHE_EXPIRY environment variable feature.
This is a follow-on to I2bc77c64b764f6c22574a30b0e5af4ca6feff29f.
Change-Id: I6db04a2c93997e594cf6d6c967fe718fc902a79b
As part of the Newton midcycle, it was discussed that it might
be nice to be able to specify the version cache timeout value
via an environment variable, rather than the current hard-coded
value.
Fixes-bug: #1596734
Change-Id: I2bc77c64b764f6c22574a30b0e5af4ca6feff29f