Addressed issue with instruction.py which prohibited inheritance of Q…

[Woody1193]

Summary

Addressed an issue whereby inheriting from QuantumRegister or ClassicalRegister would cause a QiskitError in instruction.py. This PR addresses issue #1892 .

Details and comments

Checking type-equality is brittle and should be avoided unless it is desired that only the given type be accepted. Since these classes are made available to the public, it is expected that they may eventually be inherited from.

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