Refactor utils from linuxautomaton/common into the common package

Refactor utils from linuxautomaton/common into the common package

This refactor/clean-up targets the utility functions previously found
at linuxautomaton/common.py, despite them being used across all
packages. Unused methods have been culled, while others have been
merged, split, or simplified.

All methods are extensively documented. One of the main goals of this
refactor was to improve testability. Unit tests will therefore be
implemented for these methods shortly.

The methods have been pythonified quite a bit as well. Most now make
use of exceptions, in concordance with the python philosophy of EAFP
over LBYL.

Signed-off-by: Antoine Busque <abusque@efficios.com>