QA: Allow usage of specific RAPI certificates and files

QA: Allow usage of specific RAPI certificates and files

In some situations, we want to make sure the QA runs with a certain set
of certificates, secrets, users, and the like. This patch allows the QA
to look for a directory on the master node where all of these can be
found, and transplant them into the right place. This allow cluster
creation, renew-crypto, or any other cert-affecting operation to be
tested while preserving RAPI access.

Signed-off-by: Hrvoje Ribicic <riba@google.com>
Reviewed-by: Lisa Velden <velden@google.com>