[feat] Add support for the OAR scheduler

[mahendrapaipuri]

This PR adds support to a minimal OAR backend scheduler.
Fixes #2124.

[jenkins-cscs]

Can I test this patch?

[teojgo]

Ok to test

[codecov-commenter]

Codecov Report

Merging #2129 (ca1a9af) into master (aacf20f) will decrease coverage by 0.43%.
The diff coverage is 40.21%.

@@            Coverage Diff             @@
##           master    #2129      +/-   ##
==========================================
- Coverage   85.97%   85.53%   -0.44%     
==========================================
  Files          54       55       +1     
  Lines        9651     9743      +92     
==========================================
+ Hits         8297     8334      +37     
- Misses       1354     1409      +55     

Impacted Files	Coverage Δ
reframe/core/backends.py	90.00% <ø> (ø)
reframe/core/schedulers/oar.py	40.21% <40.21%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update aacf20f...ca1a9af. Read the comment docs.

[teojgo]

@jenkins-cscs retry all

[vkarak]

Thanks @mahendrapaipuri for your PR I cannot test the backend, so my comments are related to the code itself.

[vkarak]

We would also need an entry in the documentation.

[mahendrapaipuri]

We would also need an entry in the documentation.

Added an entry in the documentation. I added a line about CI image as well. I am sorry that I forgot to push that change in that previous PR.

[vkarak]

These changes broke the unit tests for test_prepare[oar]:

E       assert {'#DW jobdw capacity=100GB',\n '#DW stage_in source=/foo',\n '#OAR --gres=gpu:4',\n '#OAR -E '\n '/private/var/folders/h7/k7cgrdl13r996m4dmsvjq7v80000gp/T/pytest-of-karakasv/pytest-111/test_prepare_oar_0/job.err',\n '#OAR -O '\n '/private/var/folders/h7/k7cgrdl13r996m4dmsvjq7v80000gp/T/pytest-of-karakasv/pytest-111/test_prepare_oar_0/job.out',\n '#OAR -l /host=8/core=2,walltime=0:5:0#OAR --account=spam',\n '#OAR -n "testjob"'} == {'#DW jobdw capacity=100GB',\n '#DW stage_in source=/foo',\n '#OAR --account=spam',\n '#OAR --gres=gpu:4',\n '#OAR -E '\n '/private/var/folders/h7/k7cgrdl13r996m4dmsvjq7v80000gp/T/pytest-of-karakasv/pytest-111/test_prepare_oar_0/job.err',\n '#OAR -O '\n '/private/var/folders/h7/k7cgrdl13r996m4dmsvjq7v80000gp/T/pytest-of-karakasv/pytest-111/test_prepare_oar_0/job.out',\n '#OAR -l /host=8/core=2,walltime=0:5:0',\n '#OAR -n "testjob"'}
E         Extra items in the left set:
E         '#OAR -l /host=8/core=2,walltime=0:5:0#OAR --account=spam'
E         Extra items in the right set:
E         '#OAR -l /host=8/core=2,walltime=0:5:0'
E         '#OAR --account=spam'
E         Full diff:
E           {
E            '#DW jobdw capacity=100GB',
E            '#DW stage_in source=/foo',
E         -  '#OAR --account=spam',
E            '#OAR --gres=gpu:4',
E            '#OAR -E '
E            '/private/var/folders/h7/k7cgrdl13r996m4dmsvjq7v80000gp/T/pytest-of-karakasv/pytest-111/test_prepare_oar_0/job.err',
E            '#OAR -O '
E            '/private/var/folders/h7/k7cgrdl13r996m4dmsvjq7v80000gp/T/pytest-of-karakasv/pytest-111/test_prepare_oar_0/job.out',
E         -  '#OAR -l /host=8/core=2,walltime=0:5:0',
E         +  '#OAR -l /host=8/core=2,walltime=0:5:0#OAR --account=spam',
E         ?                                        +++++++++++++++++++
E            '#OAR -n "testjob"',
E           }

[vkarak]

Lgtm now. I fixed the unit tests.

[mahendrapaipuri]

Thanks @vkarak for fixing unit tests.