Use active_vedors and active_zones correctly

A change was made some time ago to the Account class that moved
active_vendors and active_zones into the class from __init__.py. Both
used to be properties of the HAPI class, but became methods after the
move.

There were several places within client/zones.py that tried to access
these as if they were attributes, which caused the following error when
running the 'hapi zones' command:

    TypeError: 'method' object is not iterable

This commit replaces these attempted property accesses with method
calls, as per how they must be used now.