Install latest EPEL release

Use a little trick cribbed from [1] to install the latest EPEL
release, rather than hard-coding versions

[1] http://stackoverflow.com/questions/14016286/how-to-programmatically-install-the-latest-epel-release-rpm-without-knowing-its

Closes-bug: #1376321
Change-Id: Ib89d73d669efe2e2d61fc0b12b46395fce113386
Merge "Install latest EPEL release"
Minimize use of service token

Change-Id: I76092e9f36a4a7d45e0955efd88e53ba724af463
Merge branch 'cinder-backend-netapp' into dt-test
Merge branch 'admin-token-use' into dt-test
Merge branch 'conf-tempest' into dt-test
Merge branch 'test-service-functions' into dt-test
Merge branch 'exercise-refresh' into dt-test