After merged the patch I08c8b753972c27b4e6bbe07a8aa51e0e72fbc56d,
blazarclient can't be used with blazar_url and auth_token since this
patch only allows sessions for the initiation of client.
For backward compatibility, blazarclient should be initiated with
blazar_url and auth_token as before.
This patch enables using blazarclient with a set of blazar_url and
auth_token or session by reviving BaseClientManager class with adding
a logic to chose an auth method based on given params.