Imported Translations from Transifex

Change-Id: I713909c24064d77e7fd2062dd7ac1630ffe3372b
API: Validate and normalize address

On the API side, checks whether the supplied MAC address is formally
correct and normalize it to all lower case.

The patch also improves the docstring of the is_valid_mac function.

Change-Id: I6ae13888a9e17a10bba20acf829cbd01df535a3c
Closes-Bug: #1259269
API: Add sample() method on Port and PortCollection

Define sample() method on Port and PortCollection API objects to provide
sample data for generating the JSON and XML examples in the output of
the auto-documentation.

Also, PEP8-fy imports in port.py.

Change-Id: Ia19a2d79509d4cc820e9dea64d5c2c92dc9b3d2a
Partial-Bug: #1260337
Merge "API: Add sample() method on Port and PortCollection"
Merge "API: Validate and normalize address"
Merge "Imported Translations from Transifex"