Externalization of heat template

Reasons: preparing trove to support multi-datastores
Changes: template loading, heat-support update

This code refactors the earlier code of instance creation using heat.

- Configuration templates stored at trove/templates/(datastore_type)/config.template
- Heat templates are stored in trove/templates/(datastore_type)/heat.template
- One template per datastore type
- New parameter - ImageId
- Removed SSH key parameter
- All resources are updated according to available OS resources
  (for more details please visit heat repository).

Author: Denis Makogon (dmakogon) <dmakogon@mirantis.com>
Co-Authored-By: Nilakhya Chatterjee (SnowDust) <nilakhya.chatterjee@globallogic.com>

Change-Id: Ie6863a625e1525e152ed2886a630dc4f233be8dc
Implements: blueprint provide-custom-heat-templates-for-each-service-in-trove