Fix error when run with no arguments on Python 3

Python 3 changed the map built-in to return an iterable instead of a list.
When tested in a boolean context, this always returns True, even if it
would not return anything when iterated.

Instead of the usage being printed, this error was printed:
ERROR: 'Namespace' object has no attribute 'func'

Use list comprehension instead to ensure that an iterable isn't returned

Change-Id: Ie15f2fa8ee93ab26490e371133fa0f944430737b
Closes-bug: 1295356
Merge "Fix error when run with no arguments on Python 3"