This patch migrates designateclient to using keystoneauth Session
instead of deprecated keystoneclient's Session and plugins.

Also, this patch removes the old designateclient.auth module as it is
not used anywhere else in the code base and its purpose is overridden by
the fact that keystoneauth acts as an abstraction layer for
authentication (handling requests and reauthentication internally).

Change-Id: Ic3cc0fbb76977a04bab322ebcb1c818e75646772

Change-Id: I55a39f985fe51452ee8b892fff10787dddc7c837

Add endpoint_override keyword to v2.Client() and check for the
session argument in DesignateAdapter()
Add unit test, fix minor typos

Change-Id: I038ec7b0d1feadc9642bd47285e397b3fe84c13c
Closes-Bug: 1469739

Change-Id: I5d65508e659aa16ba0704bf1ee7d3d66a8a2d437

1. replaced dict.keys() with six.iterkeys(dict)
2. replaced map with six.moves.map

Change-Id: I4b80e12a4686fd6f5857c2322de13b1245e72083

The previous commit at [1] introduced a bug due to last
minute reordering of code, this fixes the ordering
and adds a couple of tests to verify the functionaility.

[1]: I2e3d74168976868ea1e4dd6c797f6340faa50d0f

Change-Id: Ia6f8df92b2700f63b2208290ede85f247b33bc63

edit_managed/all_tenants were moved from get_session
to the Client constructor, we should support both
for a period of time.

Change-Id: I2e3d74168976868ea1e4dd6c797f6340faa50d0f

Initializing designate client with a pre-existing keystone session
won't work as designate expects keystone session to have the
'all_tenants' and 'edit_managed' attributes:

Example code:

    keystone_session = ksc_session.Session(
      auth=keystone_auth,
      verify=True,
      cert=my_cert
    )

than later:

    self._designate_client = designate_client(
      session=keystone_session,
      region_name=region_name
    )

with that code, wrap_api_call() will raise an exception:

  AttributeError: 'Session' object has no attribute 'all_tenants'

Same goes for 'edit_managed'.

This patch moves both attributes from Keystone session to designate
Client.

Closes-Bug: 1457821
Change-Id: I13d6c9ed46406fefc8cfa5de46811e4be009f1af