Added support for ip(8) and tests for other OS samples

Refactored the self.mac_address class method.

* move ifconfig path discovery to its own method
* add discovery for ip(8)
* add Regexp to parse HWaddr - eliminate a special case
* add Regexp to parse link/ether (for ip(8))
* accept MAC address octet compression (for Solaris)

Added OS output samples and tests to verify that mac_address parses them.