Add xml support to the floating ip and router

Creating xml version for the neutron router and floatingip related
operation. The test_floating_ips.py also extended with the XML variant.

Change-Id: I5e85cd263828a127ed48db04b19fbf4d145f1d87
Clean up existing instances when not using tenant isolation

The test_list_servers_negative tests require that there are no existing
instances in the database when they run and will fail if any are found
under the primary/alternate user/tenant.

When running tempest with allow_tenant_isolation=false on a slower
system, there is a race where instances from previous tests are still
cleaning up in the background and cause test_list_servers_negative to
fail in setup.

This patch makes test_list_servers_negative block while the deleted
instances are being cleaned up in the background if running without
tenant isolation.

Closes-Bug: #1234370

Change-Id: I8519cba1fcf6ff39d69839783d07359544509db5
introduces skip_because decorator

this change introduces a skip_because decorator which accepts two args
a bug and a condition; also updates the skip tracker accordingly

Change-Id: If53f2ef81d6bddbce284267216254b467046855f
Merge "Clean up existing instances when not using tenant isolation"
Merge "Add xml support to the floating ip and router"