Fixing Nx and Graph/DiGraph issues

[BradReesWork]

Fixed a number of issues with conversion of Nx directed graphs. Fix nx tests, fixed issues with using new Graph(directed=true) but checking for DiGraph

[codecov-commenter]

Codecov Report

Merging #1882 (6ad9210) into branch-21.12 (5cc7799) will increase coverage by 0.18%.
The diff coverage is 96.38%.

@@               Coverage Diff                @@
##           branch-21.12    #1882      +/-   ##
================================================
+ Coverage         70.11%   70.30%   +0.18%     
================================================
  Files               143      143              
  Lines              8827     8863      +36     
================================================
+ Hits               6189     6231      +42     
+ Misses             2638     2632       -6     

Impacted Files	Coverage Δ
...ure/graph_implementation/simpleDistributedGraph.py	23.02% <0.00%> (ø)
.../cugraph/tests/test_edge_betweenness_centrality.py	84.33% <ø> (+1.29%)	⬆️
python/cugraph/cugraph/utilities/nx_factory.py	94.23% <87.50%> (-1.61%)	⬇️
...graph/cugraph/centrality/betweenness_centrality.py	89.65% <100.00%> (-0.18%)	⬇️
...raph/structure/graph_implementation/simpleGraph.py	74.07% <100.00%> (ø)
python/cugraph/cugraph/tests/test_bfs.py	78.14% <100.00%> (ø)
python/cugraph/cugraph/tests/test_modularity.py	100.00% <100.00%> (ø)
python/cugraph/cugraph/tests/test_nx_convert.py	100.00% <100.00%> (ø)
...ython/cugraph/cugraph/community/ktruss_subgraph.py	82.35% <0.00%> (-2.95%)	⬇️
python/cugraph/cugraph/tests/test_random_walks.py	94.36% <0.00%> (-0.08%)	⬇️
... and 16 more

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[rlratzel]

Looks good, just had some suggestions below.

[jnke2016]

Overall looks good to me. just few comments

[BradReesWork]

@gpucibot merge