Add error handlings of calling vSphere API

[hwakabh]

If user provide wrong credentials of vSphere and the program would fail with Status code 4xx from vSphere Automation SDK, the codes should reply message to the user saying wrong credentials have been set and need to fix.

Pre-checks on starting up run.py have been already implemented, so that need to modify REST-API kicker class to handle errors of target vCenter Server.