host-deploy: prepare upgrade to apache-sshd 0.11.0

since 3.1 we use internal implementation of KeyPairProvider which was
changed in future releases, in order to make transition easier drop the
internal implementation in favour of super interface.

required subset of I6943590f1c without implications.

Related-To: https://bugzilla.redhat.com/show_bug.cgi?id=1094123
Related-To: https://bugzilla.redhat.com/show_bug.cgi?id=1093882
Change-Id: I6943590f1c479e71633dcce1180028e06c9a9a17
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>