We depend on newer version of apk-tools anyways.

add -p for setting ROOT so we can debug this easier.

Tanks to nangel

Useful for bonding and bridges

We use new style bridge configuration now

This makes it slightly clearer what we are doing

we will only support apk tools so lets make things simpler

we will never support any other package manager than apk add so lets clean
up the code

- Support the ROOT env var
- use unconfigured_* functions to keep the state of which interfaces are
  configured
- Support env var INTERFACES so we can override the autodetection

a sorted list of available network interfaces thats not a part of
any bridge or bond

isin - is element in list
rmel - remove element from list
ask - Ask a question and read response
ask_until - repeat a question til a non-blank response
ask_which - repeat a question til a listed option is entered

We want avoid asking questions and in the proxy case most people will
pick 'none'.

For those who needs proxy there is still a possibility to specify the
entire proxy url in one shot, rather than asking lot of questions.

Thanks to Jim Pryor for the very useful feedback.

Not needed.

Thanks to Jim Pryor for pointing this out.