impi: execute minimal test in sanity check commands

[lexming]

This PR improves the sanity checks of impi easyblock by building the minimal MPI test program test.c and adding its execution to the sanity check commands.

I tested it with latest impi-2019.7.217-iccifort-2020.1.217.eb

• broken build with default easyconfig properly fails on sanity checks: https://gist.github.com/lexming/5ab5be4624fa0786547973a65897f40f
• sane build setting 'I_MPI_HYDRA_TOPOLIB': 'ipl' in easyconfig (which we need in our site) properly passes all sanity checks: https://gist.github.com/lexming/29ac434c5e7ad799cca986541f214a00

The tests are currently enabled for all versions as this test program is available in all non-archived releases of impi.

[lexming]

Positive test with last commit is available at https://gist.github.com/lexming/638c1af52b057f56fa90f55b7ee37c05

[lexming]

SUCCESSFUL test with impi-2019.7.217-iccifort-2020.1.217.eb at: https://gist.github.com/lexming/0b9c92be1146d7c2f9369508a2910515

[lexming]

SUCCESSFUL test with impi-2018.3.222-GCC-7.3.0-2.30.eb at: https://gist.github.com/lexming/d8171b4d9dd89bf6fed6d132f67a4d3f

[boegel]

@lexming The oldest impi versions we still have (4.x, 5.x) don't have test/test.c available, so I've added a commit to only build & run the test command for recent versions (>= 2017.x)...