Fixing iscsitarget_common.pl to correctly parse the output of iscsiadm command used for listing sessions

A SAN can expose the same iSCSI target (IQN) over multiple network interfaces (IP addresses).
In this case the target IQN is the same across all client sessions.
For a given target IQN, there cannot be multiple sessions with the same portal (IP Address).
Making portal the unique identifier for distinguishing between sessions for a given target.