Also building cpp MG tests as part of conda/CI libcugraph builds

[rlratzel]

Also building cpp MG tests as part of conda/CI libcugraph builds.

This addresses recent issues where commits were merged that broke MG test builds that were not caught in CI.

Tested locally using both a CentOS and Ubuntu gpuCI container to run the same build command in the recipe, but did not run the actual conda build command on the recipe. This required additional system packages to be installed in the gpuCI containers:
CentOS:

yum install openmpi-devel
export PATH=/usr/lib64/openmpi/bin:$PATH

Ubuntu:

apt install libopenmpi-dev openmpi-bin

[ChuckHastings]

Looks good (assuming it passes CI :-) )

[ajschmidt8]

Approved, but CI won't pass until the latest package installation changes are published. Should be done within an hour or two.

[rlratzel]

rerun tests

[codecov-commenter]

Codecov Report

Merging #1805 (5af7eff) into branch-21.10 (bf64c2c) will increase coverage by 9.80%.
The diff coverage is n/a.

❗ Current head 5af7eff differs from pull request most recent head 854c2f2. Consider uploading reports for the commit 854c2f2 to get more accurate results

@@               Coverage Diff                @@
##           branch-21.10    #1805      +/-   ##
================================================
+ Coverage         59.85%   69.66%   +9.80%     
================================================
  Files                77      139      +62     
  Lines              3547     8613    +5066     
================================================
+ Hits               2123     6000    +3877     
- Misses             1424     2613    +1189     

Impacted Files	Coverage Δ
python/cugraph/cugraph/__init__.py	100.00% <ø> (ø)
python/cugraph/cugraph/_version.py	44.80% <ø> (ø)
python/cugraph/cugraph/centrality/__init__.py	100.00% <ø> (ø)
...graph/cugraph/centrality/betweenness_centrality.py	90.00% <ø> (ø)
...thon/cugraph/cugraph/centrality/katz_centrality.py	89.47% <ø> (ø)
python/cugraph/cugraph/comms/comms.py	34.52% <ø> (ø)
python/cugraph/cugraph/community/__init__.py	70.37% <ø> (ø)
python/cugraph/cugraph/community/ecg.py	100.00% <ø> (ø)
python/cugraph/cugraph/community/egonet.py	92.30% <ø> (ø)
...ython/cugraph/cugraph/community/ktruss_subgraph.py	84.37% <ø> (ø)
... and 190 more

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[rlratzel]

@gpucibot merge

[rlratzel]

rerun tests