Fixed swift issues in installation guide

I fixed the following swift issues in the installation guide:

1) Install the keystone middleware package on proxy nodes to
   resolve dependency on standalone proxy nodes that don't
   run the keystone service.
2) Separate configuration for account-server.conf,
   container-server.conf, and object-server.conf files due
   due to unique port value for each service.

Change-Id: Ice5b5b6baa3488acc8b86f587c1efd728f034f8c
Closes-Bug: #1394025
Closes-Bug: #1394640
backport: juno
(cherry picked from commit b7034ee42ac0119ab6500fbbefa517f62fdaaec1)
Merge "Fixed swift issues in installation guide" into stable/juno