Fix common readme info for manilaclient
Fix common readme info for manilaclient

Remove cinder-specific info from readme.rst and set proper one related to
manila project.

Change-Id: If9d6fdbd335a19276cde0e88891b2c9bdb57954d
Closes-Bug: #1367215

sniperganso/python-manilaclient,sniperganso/python-manilaclient