HOT str_replace default to empty string for param

If a str_replace param cannot be resolved or is None,
substitute an empty string in order to prevent raising
an exception during validate.

Closes Bug: #1234390
Change-Id: Ica6b84cfc2157b4e1f561f737e9aa67b9f6018ca
Add some docs on how to setup Ceilometer to use Alarms

We need to use Ceilometer's mongo backend if we want to use
alarms as the sql backend is missing a feature.

Works around bug #1223710

Change-Id: Ib569cfd650ce14480496530e7bbf1b2f71a24c02
Merge "HOT str_replace default to empty string for param"
Merge "Add some docs on how to setup Ceilometer to use Alarms"