Extracting the ssh public key using cat and storing the result in a
fact has resulted in periodic failures in the collection of the key,
and thereafter the failure to appropriately place that key into the
authorised_keys file.
This patch changes the collection method to use the Ansible slurp
module which has been found to be more reliable.
Change-Id: Iac61518129536ce613e91ac894883440a8704998