[test] Add HPX hello world test

[victorusu]

No description provided.

[codecov-io]

Codecov Report

Merging #616 into master will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #616      +/-   ##
==========================================
- Coverage   91.57%   91.52%   -0.05%     
==========================================
  Files          72       72              
  Lines        8980     9142     +162     
==========================================
+ Hits         8223     8367     +144     
- Misses        757      775      +18

Impacted Files	Coverage Δ
reframe/core/environments.py	87.41% <0%> (-2.59%)	⬇️
reframe/frontend/printer.py	88.31% <0%> (-1.03%)	⬇️
reframe/frontend/cli.py	79.85% <0%> (-0.58%)	⬇️
reframe/core/schedulers/slurm.py	60.37% <0%> (-0.25%)	⬇️
reframe/utility/__init__.py	93.22% <0%> (-0.02%)	⬇️
reframe/core/modules.py	68% <0%> (ø)	⬆️
reframe/core/pipeline.py	91.72% <0%> (+0.04%)	⬆️
unittests/test_schedulers.py	98.17% <0%> (+0.06%)	⬆️
unittests/test_utility.py	98.97% <0%> (+0.15%)	⬆️
unittests/test_environments.py	67.63% <0%> (+2.96%)	⬆️

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