build/ops: do_cmake.sh: automate py3 build options for certain distros

build/ops: do_cmake.sh: automate py3 build options for certain distros

Before this patch, run-make-check.sh was setting the cmake options for
py3 build based only on the absence of a python2 binary in the system.
This was not sufficiently deterministic, and it didn't help folks who
run do_cmake.sh directly.

With this patch, we explicitly force the py3 build in do_cmake.sh, for
those OS types/versions we know need it.

Fixes: https://tracker.ceph.com/issues/37330
Signed-off-by: Nathan Cutler <ncutler@suse.com>