adding handling more mac address formats by occamengine

Until now it was assumed that user defined mac addresses in his zone file in
format: 11:22:aa:bb:cc:dd. If for example 11:22:AA:BB:CC:DD,
11-22-aa-bb-cc-dd or 1122aabbccdd was used assigning role to the new node
not worked properly. From now we try transform mac address to format
with lowe-case characters and colon as delimiter.
Merge pull request #8 from michalskalski/master

adding handling more mac address formats by occamengine