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
Allow user to specify known_hosts_file
nodelist is a dict already
Cleaning up debugs
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
Allow ec2 to look and use host keys
Document known_hosts_file
Add warning to doc
A more informative error message.

Closes #7336
consider the flo stuff to be a lost cause for now
Merge pull request #12760 from gtmanfred/develop

Change password for cloud servers if instance already exists
Fixes #12774
Correct code-block usage.
Correct usage of 'CLI Example' in documentation blocks

This mass-edit was done using the following shell command:
ack --python -l '^(\s*)CLI Example::$' \
| xargs sed -i \
's/^\(\s*\)CLI Example::/\1CLI Example:\n\n\1.. code-block:: bash/g'
Correct usage of 'Example' in documentation blocks

This mass-edit was done using the following shell command:
ack --python -l '^(\s*)Example::$' | xargs sed -i \
's/^\(\s*\)Example::/\1Example:\n\n\1.. code-block:: yaml/g'