make cfengine useful in the android termux environment

Some devices will have root (su or sudo) some will not. So the usefulness of this depends a bit on unprivileged cfengine operating well enough.

This grew out of my Summer 2018 Hackathon idea of "everyday" usage of CFEngine and I thought what better way to use it everyday than with my personal cell phone.

TODO make sub-tasks:

• packages automated testing on termux environment
• support for termux specific bits like "pkg" package management
• support for android specific bits like "am" for various purposes