engine: Setup multiple iscsi sessions with the iscsi target

Up until now the engine allowed to create single connection to the
iscsi target using only one interface.
From now on it's possible to configure iscsi multipath which will
protect against failing of the single network interface and provide
better throughput by using more than one interface.

Change-Id: I779f6dd95dfbfc2b74ad7ba3ce2271b7c9ad94db
Bug-Url: https://bugzilla.redhat.com/953343
Signed-off-by: Sergey Gotliv <sgotliv@redhat.com>