Don't read config in Manager class definition

tempest.clients.Manager loads config in the class definition
which triggers reading the config file during test discovery.
Config is loaded via the service_client_config helper, but
that's not needed anymore since service clients get their
configuration via the registry (or via a call to
service_client_config at __init__ time in case of the swift
service client).

Change-Id: Iddcfc7227f8ff1b574729a2eb8ebb63e23f09ea5
1 file changed