Add try_sudo to Pulp Smash CLI client

[Ichimonji10]

If one wants to run a command as root, the current idiom for doing so is this:

sudo = () if is_root(...) else ('sudo',)
cli_client.run(sudo + ('my', 'cli', 'command'))

It'd be far more convenient if the CLI client could encapsulate this idiom. One possible route would be to:

1. Fix Move is_root #1036
2. Update the CLI client so that it could be used like cli_client.run(('my', 'cli', 'command'), maybe_sudo=True).

If maybe_sudo is passed, then the sudo = ...; cmd = sudo + cmd idiom could be performed within the CLI client. This idiom won't work in all cases. Sometimes, sudo shouldn't be the first word in a command. For these cases, a user should still be able to use is_root, so we should make the maybe_sudo argument default to false and leave the is_root function in place.

[rochacbruno]

Addressed by #1132