Raising QiskitError

[woodsp-ibm]

While part of Qiskit, qiskit.algorithms raised, in a few places, QiskitError directly. Now there is an AlgorithmError (similar to the apps having their own exceptions) which is also used - maybe this should be raised now in those places too now that algorithms are no longer part of Qiskit. I will note AlgorithmError, and the apps' exceptions, derive from QiskitError, but it will list as the former type in a stacketrace which maybe is more desirable than directly raising QiskitError which may cause confusion now that algorithms is no longer part of Qiskit.