Make the object storage section less Ubuntu centric

The Swift section of the install guide tends to assume that the user
uses Ubuntu. This change provide more information for other
distributions.

backport: havana
Closes-Bug: #1274473
Closes-Bug: #1274405
Change-Id: I1c1fbea43d29724067185e3ab261cd20b2e0ed72
Merge "Make the object storage section less Ubuntu centric"