Changes non-functional image-name-matcher to imageId

The following tests fail (and may have passed previously as they would have been run on the default image):

Couchbase / Ubuntu 12.04 (Rackspace)
Cassandra / CentOS 6.5 (Rackspace)
All Solr tests (v. 4.7.0 is no longer available on mirrors.ukfast.co.uk, but is on archive.apache.org/dist/lucene/solr)

There is no CentOS 6.2 image available in Rackspace, hence the switch to 6.5
Images courtesy of @aledsage's CloudExplorer (PR #103)

I suggest that these issues should be picked up in a separate PR
A shame we can't use `imageNameRegex`, but I believe AWS-EC2 and Rackspace are different for whether they use name or description so can't use the same config for both. We could pass a map of additional provisioning args (e.g. `ImmutableMap.of("imageNameRegex", ".*Ubuntu.*14.04.*")` or whatever it is).

However, let's come back to that later.

If I'd been fixing this, I'd have included a `TODO` comment saying about it failing (with the date), and about it previously not being tested properly. But I'm fine merging this as is now.