Added get_cpu_speed to tools.systemtools

Returns the maximum cpu speed in MHz.
get_cpu_speed: make code python 2.4 compatible
Cleanup: use constant UNKNOWN instead of string
Merge branch 'develop' into test
fix remarks in systemtools.py + enhancements and style fixes, add unit tests for systemtools.py
fix os.path.exists lines in systemtools.py
revert back to try-except when reading system files in systemtools.py
Merge pull request #694 from wpoely86/cpuspeed

Added get_cpu_speed to tools.systemtools