don't use pip to install mympingpong + add sanity check command to catch broken installation

[boegel]

(created using eb --new-pr)
shouldn't use pip because it breaks the vsc.* namespace (see hpcugent/vsc-install#68)

[lexming]

Test report by @lexming
SUCCESS
Build succeeded for 8 out of 8 (2 easyconfigs in total)
node101.hydra.os - Linux centos linux 7.8.2003, x86_64, Intel(R) Xeon(R) CPU E5-2680 v2 @ 2.80GHz, Python 2.7.5
See https://gist.github.com/7ea618c99e8f497cd8afb4e2f49ba54f for a full test report.

[lexming]

Test report by @lexming
SUCCESS
Build succeeded for 8 out of 8 (2 easyconfigs in total)
node368.hydra.os - Linux centos linux 7.7.1908, x86_64, Intel(R) Xeon(R) Gold 6148 CPU @ 2.40GHz, Python 2.7.5
See https://gist.github.com/67b370ff2a03778dd804341d8d8ddc92 for a full test report.

[boegel]

Test report by @boegel
FAILED
Build succeeded for 9 out of 13 (2 easyconfigs in total)
node3104.skitty.os - Linux centos linux 7.8.2003, x86_64, Intel(R) Xeon(R) Gold 6140 CPU @ 2.30GHz, Python 3.6.8
See https://gist.github.com/f00d91be166311a9d7747392fbff588e for a full test report.

[boegel]

Test report by @boegel
FAILED
Build succeeded for 5 out of 7 (2 easyconfigs in total)
node2498.golett.os - Linux centos linux 7.8.2003, x86_64, Intel(R) Xeon(R) CPU E5-2680 v3 @ 2.50GHz (haswell), Python 2.7.5
See https://gist.github.com/a412877a5af84fe3131b00f1ec2713b3 for a full test report.

[boegelbot]

@boegel: Tests failed in GitHub Actions, see https://github.com/easybuilders/easybuild-easyconfigs/actions/runs/339419106
Output from first failing test suite run:

FAIL: test_changed_files_pull_request (test.easyconfigs.easyconfigs.EasyConfigTest)
Specific checks only done for the (easyconfig) files that were changed in a pull request.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test/easyconfigs/easyconfigs.py", line 807, in test_changed_files_pull_request
    self.check_python_packages(changed_ecs, added_ecs_filenames)
  File "test/easyconfigs/easyconfigs.py", line 644, in check_python_packages
    self.assertFalse(failing_checks, '\n'.join(failing_checks))
AssertionError: 'use_pip' should be set in vsc-base-2.8.3.eb
'use_pip' should be set in vsc-install-0.17.1.eb

----------------------------------------------------------------------
Ran 10810 tests in 926.956s

FAILED (failures=1)
ERROR: Not all tests were successful.

bleep, bloop, I'm just a bot (boegelbot v20200716.01)
Please talk to my owner @boegel if you notice you me acting stupid),
or submit a pull request to https://github.com/boegel/boegelbot fix the problem.

[jfgrimm]

Test report by @jfgrimm
FAILED
Build succeeded for 7 out of 13 (4 easyconfigs in total)
himem06.pri.viking.alces.network - Linux CentOS Linux 7.9.2009, x86_64, Intel(R) Xeon(R) Platinum 8160 CPU @ 2.10GHz (skylake_avx512), Python 3.6.8
See https://gist.github.com/jfgrimm/9bc5491db13da7ad453cbc8906853b77 for a full test report.

[akesandgren]

Closing this PR, since it (only) uses deprecated toolchain versions,
see https://docs.easybuild.io/policies/toolchains .