test_environment.sh: now removes properly the hard disk images
test_environment.sh: stick to a bash convention

Use only tabs when indenting instead of spaces, and set a maximum number of
characters per line of 79.
WIP: use absolute paths
fixup! test_environment.sh: fix the routing towards the virtual machine
test_environment.sh: added extra logging for bebugging

In order to add debuggin, the way the functions return values must be
changed. This is because, until now, they printed out the result.

Now, that wouldn't be working because of the extra lines that are printed.
As a convention (at least in this file), the returned value will go in the
last parameter specified in its call.