Fix error trace induced by dhcp test actions

Once the agent is removed, we are unable to deallocate
dhcp resources for the port until the entire network is
torn down; this is fine, but by doing so we cause Neutron
Server to emit a log error.

This patch simply deletes the port before doing the
disassociation, however a cleaner way to deal with this
would be to avoid relying on port creation to trigger a
network scheduling, though, this would require a more
elaborated fix.

Closes-bug: 1292242

Change-Id: I187d8dd707d67eb39446a5558913331310bd1f47
Add server to clean up even in case of errors

In the case of instance build times out it would never been added to cleanup so
we put it on the list before wait for it get ready.

Fixes bug #1292641

Change-Id: Id030457cfe038849b81008de18b5f93fc024a47e
Merge "Add server to clean up even in case of errors"
Merge "Fix error trace induced by dhcp test actions"
Merge commit 'refs/changes/65/81565/2' of git://gold.eng.hq.xensource.com/git/github/openstack/tempest into tmpbranch