The idea is that if you set some branch then it is most probably not
deploy signed branch and so we should include test key. On the other
hand if it is a deploy branch then this is not huge problem. The key
would be removed with first updater run.

This modifies basic script to use server specific bootstrap script.

Updater is now configured little bit differently. This new default
configuration file reflects that.

This also fixes problem where variables in m4 were always defined and
because of that some parts were always generated to be there even if
they were empty.

There should be default value set for branch so no branch option
requirement.

This changes output name to format that is consistent with one used in
3.x release cycle for Turris Omnia.

This is better idea as having #!/bin/bash -e is fragile. Anyone can run
this script with bash -x file and that way unintentionally disable -e
flag.