Introduce Opts for IP addresses

In order to validate correct input values for IP addresses new Opt was
introduced. Validation is done on parsing level so there is no need to
explicitly check for valid ip address in the code.
Requirement for netaddr package was added.

DocImpact

Change-Id: I9adc30d9b989e8c636fefd435885c4c363ca540c
Partial-Bug: #1284684
Fix flaws in methods' docstring

Change-Id: Idaebbc5702daeabc22b44672ce7b7d301a725871
Merge "Fix flaws in methods' docstring"