Tests around v4 authentication - clients [JIRA: RCS-116]

[Basho-JIRA]

• Client side implementation in basho/erlcloud
  • can steal from basho-labs/rinamo
    https://github.com/basho-labs/rinamo/blob/master/src/rinamo_auth_keystone_v2.erl#L45-L47
• more v4 tests by various client tests
• Use v4 (optionally?) in basho_bench cs driver