Hi, CI runs now OST basic-suite-master periodically with data center and
cluster versions different from the default one on master.  That tests
changes in master for breakages when run in older version compatibility
modes.  Contingent failures are reported to infra.

If you make an OST test known not to run on older cluster versions
(e.g. < 4.1), you should mark the test with a decorator such as

  @versioning.require_version(4, 1)

You can also distinguish cluster version dependent code inside tests by
calling

  versioning.cluster_version_ok(4, 1)

See examples in basic-suite-master.

You can run basic-suite-master with a different data center and cluster
version manually on your computer by setting OST_DC_VERSION environment
variable, e.g.:

  export OST_DC_VERSION=4.1
  ./run_suite.sh basic-suite-master

Barak, it's currently possible to request OST run on Gerrit patches.
I was asked whether it is also possible to request an OST run with a
non-default cluster version(s).  Is it or not?