test_live_block_migration cleanup

* The Test case names does not needs numbers
* test_invalid_host_for_migration not a positive test
* It is an admin Test (BaseComputeAdminTest)
* getting hosts_client as the other test does

Change-Id: I95f013983d173008d7b1437fda2c247ef81c68ee
Update stress tests to properly use tempest.config

When tempest.config was switched over to using oslo the stress tests
weren't updated with those changes. Also subsequent changes to the
tempest options were not updated in the stress test suite. This left
the stress tests unusable because it couldn't get the needed
information from config. This commit updates the stress test suite
to properly use tempest.config. It also adds a new section to the
config file for stress test specific options.

Fixes bug 1133012

Change-Id: I1b0c726f53dc0e3e0777e27af3e860d35029f958
Merge "test_live_block_migration cleanup"
Merge "Update stress tests to properly use tempest.config"