Implement aliases for common actions

[pvalena]

Actually what I expected would be for tmt to know such aliases.

Where you recommend alias reserve=... to create command reserve I'd expect to have $ tmt reserve built in, or $ tmt start etc.. (So it's all fine, except I'd like tmt to actually implement it, not just recommend.)

Originally posted by @pvalena in https://github.com/psss/tmt/pull/404#issuecomment-707632170