Create a separate snapctl package

[farshidtz]

To Do:

• get
• set
• unset
• start
• stop
• services
• restart

[farshidtz]

Let's review and get this merged to have the testing environment and the new function for use by other parallel work. The remaining tasks can be done in separate PRs.

[farshidtz]

@siggiskulason I've added the set functions.

[farshidtz]

@siggiskulason I've implemented the services functions needed for the new config options API.

[siggiskulason]

LGTM. Tested this according to the instructions and everything ran as expected. The code looks good as well, but as this is still a work in progress I won't do a code review until it's all done.