Add -override Option to Control a Group of Instances

[iversond]

There may times when you want to force a group of servers to start or stop outside a predefined schedule. This could be a group of lab servers used for training that you want to control ad-hoc. You can add a defined tag Schedule.Override with any value to the instances and reference them with the -override parameter.

For example, you have the tag Schedule.Override: labservers set on instances, you can start those instances using this command.

python3 AutoScaleALL.py -a Up -override labservers

[iversond]

This idea and much of the code was from @kbens - I retrofitted into the current code base and tested it.