(maint) Release hosts to the vcloud pooling api

Our configurations now uses Scott's vcloud pooling api, so rather than
attempt to destroy them directly through vsphere (the code for which was
no longer working with current rbvmomi anyway) we are submitting them to
the pooling api for deletion.
(maint) Remove unused rsync for preserved acceptance test reruns

Package re-installation and rsyncing of local code changes while
re-running acceptance tests on preserved vms is something we aren't
doing. A better solution for the cycle of acceptance testing against
local changes is to use a git install against a local git daemon (see
the docs/acceptance_tests.md) to test against changes you have checked
in locally.
(maint) Pin to Beaker 1.7 and default to preserve_hosts onfail

Beaker can now be set to preserve hosts if the acceptance run fails.  We
are now defaulting to that for ci and manual testing, and pinning to
Beaker ~>1.7.0, so any release on the 1.7 line.
Merge pull request #2339 from jpartlow/maint/master/acceptance-harness-releases-pooled-hosts

Maint/master/acceptance harness releases pooled hosts