Search configuration files in all directories upwards from the script directory

The idea is to allow having a project specific configuration in the
project's repository as well as user specific one in the home directory.
Remove $server configuration variable

Can be replaced by putting --server option to %targets configuration.
Remove grub_keys configuration option

I have no use case for this option and it never worked reliably.
Remove $iprelay configuration variable

Also improve --on/--off handling.
Remove $pulsar_mac configuration variable
Simplify scons handling
Simplify qemu handling
Don't dump log messages to the config file; better indentation of the config file