Handle exception when BQM is passed to DQM sampler

[Abdullahjavednesar]

Closes #375

Before
BinaryQuadraticModel objects when passed to DQM sampler, raised an exception which wasn't informative.

>>> import dimod
>>> from dwave.system import LeapHybridDQMSampler
>>> bqm = dimod.BinaryQuadraticModel('SPIN')
>>> LeapHybridDQMSampler().sample_dqm(bqm)
...
AttributeError: 'BinaryQuadraticModel' object has no attribute 'num_variable_interactions'

Now (after fix)

>>> LeapHybridDQMSampler().sample_dqm(bqm)
TypeError: Expecting DiscreteQuadraticModel object, got <class 'dimod.binary.binary_quadratic_model.BinaryQuadraticModel'>

[Abdullahjavednesar]

Hi @arcondello, can you please take a look!

[Abdullahjavednesar]

Addressed both the comments. Thanks for the review!

[codecov-commenter]

Codecov Report

Merging #444 (ff432b4) into master (4fa4b27) will decrease coverage by 2.93%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #444      +/-   ##
==========================================
- Coverage   90.52%   87.59%   -2.94%     
==========================================
  Files          22       22              
  Lines        1520     1523       +3     
==========================================
- Hits         1376     1334      -42     
- Misses        144      189      +45     

Impacted Files	Coverage Δ
dwave/system/samplers/leap_hybrid_sampler.py	61.97% <100.00%> (-13.75%)	⬇️
dwave/system/samplers/clique.py	77.35% <0.00%> (-5.04%)	⬇️
dwave/system/samplers/dwave_sampler.py	84.14% <0.00%> (-3.05%)	⬇️
dwave/system/composites/embedding.py	96.00% <0.00%> (-1.15%)	⬇️

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[arcondello]

Hi @Abdullahjavednesar , sorry for the very long delay. Any chance you can rebase this against the current master branch? We can also do it on our side