Fix copying control-flow bodies in builder interface

[jakelishman]

Summary

There are a few places where the structure of an element of
QuantumCircuit.data is specifically assumed to be

Tuple[Instruction, List[Qubit], List[Clbit]]

rather than the more abstract

Tuple[Instruction, Sequence[Qubit], Sequence[Clbit]]

For performance reasons, the control-flow builders used tuples to store
their arguments internally, because this prevents any copying being
necessary, and allows the arguments to be put in sets. Now, in lieu of
changing the QuantumCircuit data structure to be more abstract, which
would have performance implications, or to require the tuples, which may
create more bugs, we just make the builder interface convert its tuples
to lists on output.

Details and comments

A relatively hidden bug, but a bug nonetheless, and fixing this will make it much easier for Aer to write its test cases for 0.10. @hhorii.

Fix #7367.

[coveralls]

Pull Request Test Coverage Report for Build 1551115436

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• 5 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.008%) to 83.094%

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Files with Coverage Reduction	New Missed Lines	%
qiskit/extensions/quantum_initializer/uc.py	2	88.65%
qiskit/pulse/library/waveform.py	3	89.36%

Totals
Change from base Build 1550571358:	-0.008%
Covered Lines:	51667
Relevant Lines:	62179

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💛 - Coveralls

[kevinhartman]

LGTM!