Improve devstack install script

Do not fail on some non-fatal errors:

 * user rally already exists
 * ~/.ssh directory already exists
 * iptables is not available

Change-Id: Ibc937592e40097720be42d6442ec1c78f04722db
Print task information when creating task from CLI

Summary line is printed when task has been created but not started,
detailed information is printed once the task has completed.

Change-Id: I8a3cbb81d7fccffe158517d3023ad47d28d7ebc1
Trello: https://trello.com/c/wJbH8DqG
Add keystone host unreachable checks

Raise HostUnreachableException if the property auth_url is wrong

Implements blueprint keystone-auth-url-wrong

Change-Id: Idf2a07b1535a4a3c53814a1a55959afc59caefe2
Merge "Improve devstack install script"
Merge "Print task information when creating task from CLI"
Merge "Add keystone host unreachable checks"
Create rally deployment from OS_* environment variables

This saves users from creating dummy config json files when they already
have an openrc for use with the other openstack clients.

Change-Id: I487af60e0c6a5eadfc12f04fbba9c4a4186740e0
Trello: https://trello.com/c/5ZkMb9zL