Rework functional test case infrasatructure

Rework functional test case infrasatructure

To support multi-instance, two new classes were made:
Stack - represents a stack
Instance - represents an instance

For multi-instance stacks, create multiple Instance objects
for each instance in the stack.

For each instance in a stack, an instance object can be created which
helps validate the individual instance sets up properly.

test_WordPress_Single_Instance_With_EBS.py fails - see issue #226

Change-Id: Iddec87cd1332a9b5796c5c7e7d382ef723c3544e
Signed-off-by: Steven Dake <sdake@redhat.com>
Signed-off-by: Tomas Sedovic <tsedovic@redhat.com>
Signed-off-by: Ian Main <imain@redhat.com>