Update HamiltonianGate path and add tolerance to PulseBackend (backport #1280)

[mergify]

This is an automatic backport of pull request #1280 done by Mergify.
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Changes to be committed:
	modified:   qiskit_experiments/test/pulse_backend.py
	modified:   releasenotes/notes/0.3/cleanup-cr-hamiltonian-experiment-7f47c51d26941f16.yaml
	modified:   test/library/calibration/test_rabi.py
	modified:   test/library/calibration/test_rough_frequency.py
	modified:   test/library/characterization/test_cross_resonance_hamiltonian.py
	modified:   test/library/characterization/test_multi_state_discrimination.py

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	both modified:   qiskit_experiments/test/__init__.py
	deleted by us:   test/library/calibration/test_half_angle.py
	both modified:   test/library/calibration/test_rough_amplitude.py

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[coruscating]

Not needed since failing tests were addressed in #1365.