At least for cinder for now, allow a consumer of get_legacy_client to
express the minimum version they find acceptable. This will use
cinder_client logic to figure out the version from the url.
As a follow on, expand this to all of the clients and make it support
microversions for the clients that support microversions. (Right now
it's just going to be major versions, so min_version=1 will throw an
exception if the cinder service returns a v1 endpoint.
Also, because we override the volume/volumev2/volumev3 service type
stuff, we need to do extra special logic in get_session_endpoint to try
all three in the case where do not have a configured api_version.
Change-Id: I7b6b3588fec9a6be892cf20d344667f0b9a62f0a
b2f7ceadb1