Fix password field name

Fix password field name according to OpenStack documentation
http://api.openstack.org/api-ref-identity.html#identity-v2.
Example of json request
{
  "user": {
    "username": "jqsmith",
    "email": "john.smith@example.org",
    "enabled": true,
    "OS-KSADM:password": "secrete"
  }
}
Allow Acepted response status

On call nova.servers().boot(serverForCreate).execute() OpenStack return Accepted status.
Disable fail on unknown properties

OpenStack could have specific extensions which add fields to response, to avoid unexpected fields just ignore them.
Fix/implement create image
Merge pull request #127 from kovaliovs/master

Fix password field name