support new HTTP microversion header

support new HTTP microversion header

According to API working group guidelines:
https://review.openstack.org/#/c/243414

microversion headers should be of the form:
OpenStack-API-Version: [SERVICE_TYPE] 2.114

i.e OpenStack-API-Version: volume 3.22

Two extra headers are always returned in the response:

    OpenStack-API-Version: [SERVICE_TYPE] version_number
    Vary: OpenStack-API-Version

note: Servers must be prepared to deal with multiple
  OpenStack-API-Version headers. This could happen when a client
  designed to address multiple services always sends the headers it
  thinks it needs. Most Python frameworks will handle this by setting
  the value of the header to the values of all matching headers,
  joined by a ',' (comma). For example ``compute 2.11,identity
  2.114``.

Closes-Bug: #1551941
Change-Id: I658e54966c390b41e3b551dd9827606c2e013511