Wait until pingable after upgrading.
Allow specifying the upgrade_version on the command line.
Whitespace cleanup and reformatting.
Exclude backend and upgrade_version from the test metadata if unspecified.

This removes the problem where upgrade_version is set to undefined and
then included in the test metadata, overriding the test's defaults.
Merge pull request #159 from basho/sdc-fix-upgrade-race

Fix race in upgrades