Email notification changes

Hi,

We've made the following changes:

* CloudFormationChaosMonkey class to enable email notifications when
no-suffix group names are used.

* Modified BasicChaosMonkey and BasicChaosEmailNotifier classes to enable
global email notifications. eg.
```simianarmy.chaos.notification.global.receiverEmail = test@email.com```
is used to enable global email notifications. Added corresponding unit
test.

* Refactored TestChaosMonkeyContext to remove duplicate code