core: configurable ssl protocol

We need to make ssl protocol configurable.

I tested 3.5 engine and vdsm with all combinations (sslv3, tlsv1) and
there were no issues.

I tested 3.0 engine with 3.5 vdsm and noticed that when tlsv1 was set on
vdsm side the communication failed with wrong protocol version.

I tested 3.0 vdsm with latest engine (tlsv1) and it worked after hacking
host-deploy.

Change-Id: I33a33c15e8a995eb8de7d5131b3dbadc6191f873
Signed-off-by: pkliczewski <piotr.kliczewski@gmail.com>
Bug-Url: https://bugzilla.redhat.com/1154184