Add and Correct info on add user API usage

Page coresponding to source file change:
http://docs.openstack.org/api/openstack-identity-service/2.0/
content/POST_addUser_v2.0_users_User_Operations_OS-KSADM.html

Source of info:
http://docs.rackspace.com/auth/api/v2.0/auth-client-devguide/
content/POST_addUser_v2.0_users_User_Calls.html

http://docs.openstack.org/grizzly/openstack-compute/install/
yum/content/setting-up-tenants-users-and-roles-manually.html

https://computing.seas.harvard.edu/display/CLOUD/
Add+a+user+to+OpenStack

http://turing.suse.de/~aj/cli-reference/content/
keystoneclient_commands.html

Corrections(tested with DevStack installation)

username/user should be name
the only required field

Optional fields:
password / OS-KSADM:password

enabled <true|false>

tenantId
warning tenant/tenant-id/tenant_id won't work

email
customized fields

Change-Id: I9db725a4138e0161bf0a0c2b8d86b7424aa3099a
Closes-Bug: #1171510
Merge "Add and Correct info on add user API usage"