Fix various improvements

Sorry for a somewhat messy commit.

The --*-machine commands has been removed. We're keeping
list_*_machines for now, so that we can merge them into their
respective client functions (list_*_clients doesn't actually go
through the machines, but only checks the configuration files).

Implemented `is_client_online' for Android; uses ADB instead of SSH.

Improved `get_guest_os_for_client_android'.

Some clarifications has been made; variable name changes, change of
messages, and some prettier printing for the output.

Unnecessary `for' loops has been removed.
Merge branch 'master' of github.com:tis-innovation-park/vmm