Set root password for nova vms

If the server is already created and just needs to be bootstrapped,
change the password using the api to something set by secure_password
change password if instance already exists Openstack
pylint fixes
nodelist is a dict already
store the password for logging into the server
Add change_password option for openstack providers

Document as well
add change_password to openstack
fix pylint error
Merge pull request #12760 from gtmanfred/develop

Change password for cloud servers if instance already exists