Make text in Project Overview - Limit Summary section consistent

It removes 'Available' prefix from 'Available Volumes' and 'Available
Volume Storage' to make them consistent with others; e.g. 'Instances',
'VCPUs', 'Security Groups' etc.

Change-Id: I2d901348afa17b3393e7759871b1609c64f73dc2
Closes-Bug: #1268800
Merge "Make text in Project Overview - Limit Summary section consistent"