Avoid masking an assert failure with a KeyError Exception

This patch does not address the underlying issue as to
why the key was not in the data dictionary, but it serves
the purpose of getting a better error message due to the
failure in meeting the pre-conditions to the test.

Change-Id: I507a34456e8d047728bb7c1d1e5d189e3d00e7c1
Related-bug: #1268274
Log ip Information on ssh failures in the minimum scenario

The minimum scenario frequently have ssh connectivity issues,
 both with neutron and nova-network. Logging the ip and iptables
state at the failure, can help in finding the root cause sooner.

Change-Id: I3205541f96810b5b88e7c5ac3000fe1a1294ec65
Merge "Avoid masking an assert failure with a KeyError Exception"
Merge "Log ip Information on ssh failures in the minimum scenario"
Merge commit 'refs/changes/20/75120/6' of git://gold.eng.hq.xensource.com/git/github/openstack/tempest into tmpbranch