Add function to migrate user without syncing passwords
Fix checksum handling for images, fix existing secgroups logic
Correct dict key name for tenant ID when creating users
Raise if trying to migrate service user
Raise if trying to migrate service tenant
Add users resource migration from cli
Add support for 'users' optional resource argument

With '--resource users' migrate only users (and tenants), not
touching other resources
Minor issues with dict and optional attributes to users.create
call
Merge branch 'user-migration'