Make ProviderFactory.get_provider more simple

Provder name can be found in provider config, so first argument of get_provider
is not necessary. Now provider can be created by calling
ProviderFactory.get_provider(provider_config) instead of
ProviderFactory.get_provider(provider_name, provider_config)

Change-Id: Idc579ef6c362b4180fa4f24201363bc0b8d3ac33