Migrate test_encrypted_cinder_volumes to tempest client

Migrate the test parent class of EncryptionScenarioTest from
OfficialClientTest to ScenarioTest. And some helper functions are
migrated to ScenarioTest.

Change-Id: I33bcd8d0d787ce67617e6ef07652fe1ca1b7e111
Partially-implements: bp:tempest-client-scenarios
Support lack of ephemeral volumes for baremetal

The agent driver in Ironic does not yet support ephemeral volumes.
This change allows tempest to test Ironic with the agent driver
by skipping ephemeral volume checks if the ephemeral volume size
is 0.

Change-Id: I9525d1c75007555d368a2aa66ab840f41b584a30
large ops test should be derived from OfficialClientTest

Scenario test_large_ops runs on gate-tempest-dsvm-large-ops
& gate-tempest-dsvm-neutron-large-ops jobs.

This test case boot VM with security grp by requesting the same from
Nova. Nova can behave as proxy in case neutron is enabled.

This is needed to migrate this test from official
client to tempest client as _create_security_group() fucntion
which request nova to create sec grp can not be used via
NeutronScenarioTest.

Partially-implements: bp:tempest-client-scenarios

Change-Id: I7b69811b49caf3aec5983e27862ce955aadf958a
Migrate test_large_ops to tempest client

This patch migrate the test_large_ops scenario tests
from official client to tempest clients.

Partially-implements: bp:tempest-client-scenarios

Change-Id: I417fba287f212667e08b3b246f222b60249e47b1
Merge "large ops test should be derived from OfficialClientTest"
Merge "Migrate test_large_ops to tempest client"
Merge "Migrate test_encrypted_cinder_volumes to tempest client"
Merge "Support lack of ephemeral volumes for baremetal"
Merge branch 'master' of https://github.com/openstack/tempest