Updates root-enable & root-show help messages

Reasons:
- Help message for root-enable does not gives complete information, it
  misses that API also resets root, on existence.
- Current help message for root-show makes it feel like current status
  of root user is fetched, but instead we are also returning True for
  historical root access enabled.

Changes:
- Updated the root-enable and root-show API help message.
- Updated README for updated help messages.

Change-Id: Ide7c331bdfe5437e6966f6cd4f331cb3b22d0c3f
Closes-Bug: #1277308
Add 'slave_of' option for enabling replication

Add a new create option (--slave_of) that can be used to enable
replication and configure the newly created instance as a slave of the
specified existing instance.

DocImpact Introduces new option when creating an instance.

partially Implements: blueprint replication-v1
Change-Id: Idf22d3d9e676138969cbdf3afd4903b8e475c313
Merge "Updates root-enable & root-show help messages"
Merge "Add 'slave_of' option for enabling replication"