Change "_savanna_" image properties to "_sahara_"

The PROP_USERNAME, PROP_DESCR, and PROP_TAG values used for
labeling images have been changed to use "_sahara_" prefixes
instead of "_savanna_"

Partial-Implements: blueprint savanna-renaming-service
Change-Id: I63c7316868e6721b0bdf31ac648c4b203755ba00
Change 'savanna' references in tools

Partial-Implements: blueprint savanna-renaming-service
Change-Id: I5dfdeb41f290dd5679ca4ba53c7dd7c79e9886bd
Change remaining savanna namespaces in setup.cfg

* savanna.cluster.plugins, savanna.infrastructure.engine, savanna.remote
* Remove the 'savanna ', only support 'direct' and 'heat'
* Change 'base' in openstack-common.conf to 'sahara'

Partial-implements: blueprint savanna-renaming-service
Change-Id: I82f7f98794b86a305aff544eb6f77f1a8810d9d7
Merge "Change "_savanna_" image properties to "_sahara_""
Merge "Change 'savanna' references in tools"
Merge "Change remaining savanna namespaces in setup.cfg"