More lambda-friendly variants for runRemotely

[jglick]

I have discovered a usability flaw in #882, that

rr.runRemotely(r -> someStatement());

(where someStatement is a method returning void) does not compile, as javac tries to use Step2 when Step was meant. You can work around it via

rr.runRemotely((RealJenkinsRule.Step) r -> someStatement());

or

rr.runRemotely(r -> {someStatement();});

but both are awkward. It would be better to introduce aliases like run(Step) + call(Step2) which would more identify the expected lambda type.