Make it easy to use the e2e tests to test upgrading a running master

by adding support for testing official release versions and writing a simple script to first bring up and test the old version before upgrading it and testing it again. Related to supporting in-place upgrades of masters (#2524).

The downsides of this are that by default it uses the e2e tests from HEAD, which may not be expected to pass on an old cluster, and that it uses the client binaries from head. I can send a follow-up to fix the client binaries issue, but don't have anything planned for supporting old e2e tests.

I'm not sure how our Jenkins setup is configured, but it'd be nice to get something along these lines added to it in the future.
Optional suggestion: call tar directly instead of telling bash to call tar. Make something like the "run" command that you removed that takes a []string of args.

Otherwise, if you parameterize runBash according to my other suggestion, it'd be good to have a runRawBash command that didn't source a bunch of kubernetes specific stuff when all it needs to do is call tar.