[test-runner] Show help on error
[test-runner] Show help on error

Help is shown if no arguments are provided.
Also additional formatting was added.

Closes-bug: #1508420
Closes-Bug: #1508422

Change-Id: Idf3b2bf0d5cbbc134795bcd2d1b24cf694f1975e

openstack/murano,satish-avninetworks/murano,olivierlemasle/murano,NeCTAR-RC/murano,NeCTAR-RC/murano,olivierlemasle/murano,DavidPurcell/murano_temp,olivierlemasle/murano,DavidPurcell/murano_temp,NeCTAR-RC/murano,DavidPurcell/murano_temp,olivierlemasle/murano,satish-avninetworks/murano,satish-avninetworks/murano,satish-avninetworks/murano,openstack/murano,NeCTAR-RC/murano,DavidPurcell/murano_temp