Aims at fixing two issues: we had an unless clause which was only
checking if the secret was already defined, not if the value for
the secret was set; when providing the value for the secret, we
were mistakenly referring to the secret by its XML dump instead of
its UUID.
Change-Id: I513599735e974c07a6a0e46fd319930740f259cc
Closes-Bug: #1425601