Needed because salt-cloud will attempt to load them even if they are
filled with invalid default values, creating error spam.

This obsoletes the salt:cloud:folders and salt:cloud:providers pillar
entries. Provider keys have been moved to /etc/salt/pki/cloud.

These aren't intended to function; they're here to allow the use of
file.recurse on the provider folder, without requiring the user
to provide pillar data for templates they're not using.

Most include do not expect salt to be something else than the usual salt
variable giving access to all the salt modules. Instead we use cfg_salt.
And for consistency we rename the master/minion variables to
cfg_master/cfg_minion too.