use assertDictAlmostEqual in test_mapper

[ajavadia]

Seems like one test case was missed in #380 when we updated tests to allow tolerance intervals instead of exact comparisons.
This PR covers that.

Description

Motivation and Context

How Has This Been Tested?

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Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[chriseclectic]

I think for this circuit the ideal counts should be shots / 2. Can you change this block to:

shots = 1024
result = self.qp.execute("test", backend="local_qasm_simulator",
                                 coupling_map=coupling_map,
                                 seed=self.seed, shots=shots)
counts = result.get_counts("test")
target = {'0001': shots / 2, '0101':  shots / 2}
threshold = 0.025 * shots

and check if the test still passes (you might need to increase the shots or adjust the threshold a little bit)