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.
Closes-Bug: #1506291
Change-Id: I3ba5cdc944f38c67762860dc0d06bd5c35eeb269