iso-tester: test busy CIG error does not drop existing connections

iso-tester: test busy CIG error does not drop existing connections

A second connection made with same CIG while the CIG is busy, shall not
disconnect the first already existing connection.

Add test for this:

ISO Connect2 Busy CIG 0x01 - Success/Invalid

This was the original intent of "ISO Connect2 CIG 0x01 -
Success/Invalid", but the busy check should not be made synchronously in
connect() (to maintain ordering with Remove CIG etc), but must be done
in hci_sync. So the test needs to check the error async and explictly
that the first conn is not dropped.