Refactor call of command inside build directory into separate function
Add support for "-f" option to specify Blubberfile to use
Add message if command could not be recognized
Add check for Linux environment, and disable poky execution if none is found.
Improved usage decription output
Rework platform identification code
Add query_yes_no, taken from http://stackoverflow.com/a/3041990
(slightly modified for python3)
Add platform validation code, mostly functional for Debian/Ubuntu,
other distributions are recognized but not yet supported
Add "validate" command to test and possibly fix the build platform dependencies.