Correct documentation related to protected properties

Fixes bug 1233303

Specified conditions under which glance api will not start
successfully.

DocImpact

Change-Id: I8498e9e51f5c7e0d411379c0574c0b8e300f77c2
Add call to get specific image member

Fixes bug 1233806

Add GET call to get a specific image member. Makes it easier to
check image member status

DocImpact

Change-Id: I63039bc15d2045fbceb71cae56225a9ee9eecd51
Merge "Correct documentation related to protected properties"
Enable tasks data model and table for async worker

Add tasks data model and table for async worker to
store the tasks data persistently.

Partially implement blueprint async-glance-workers

Change-Id: I2b2d70295da4905bf75cffc2b2eadec174d1abfc
Merge "Add call to get specific image member"