x.py feature parity with cargo (alias)

[pickfire]

cargo currently supports cargo t, cargo b and a few others even though not so discoverable (rust-lang/cargo#6104 (comment)).

It would be good to let x.py supports the aliases supported by cargo, such as ./x.py t, ./x.py b and such.

This issue has been assigned to @mibac138 via this comment.

[mibac138]

@rustbot claim