enhance Amber easyblock for AmberTools

[mboisson]

This PR allows a few tings

1. For my build, CMake failed to find the fortran headers for NetCDF unless I make their location explicit through NetCDF_INCLUDES
2. CMake will not automatically find FlexiBLAS. Defining the libraries
3. Allows to overwrite the INSTALL_TESTS and COMPILER options. In particular, when compiling with GCC on our stack, if I don't set COMPILER to GNU, disable usempi (to get serial compilers for serial code) and enable MPI through the CMake option, it fails to build. ~4) Disable tests when building AmberTools, as not all the binaries are included.~

[mboisson]

PR https://github.com/easybuilders/easybuild-easyblocks/pull/2720 addresses some of the same points as this PR, but not all of them. In particular, it does not disable tests for AmberTools, and so the build of Ambertools fails

[akesandgren]

PR https://github.com/easybuilders/easybuild-easyblocks/pull/2781 makes sure the tests are run the correct way and should eliminate that problem.

[boegel]

@mboisson Can you sync this PR with current develop?

[mboisson]

Done

[akesandgren]

The NetCDF-Fortran problem is solved with AmberTools-20_cmake-locate-netcdf.patch but doing it directly in the easyblock might be beneficial. FlexiBLAS is solved with AmberTools-21_CMake-FlexiBLAS.patch which I think is the more correct way.

Thoughts on the above two @mboisson ?

(And the testing is finally solved with the latest easyblock+easyconfigs+patches, apart from a few remaining test failures)

[mboisson]

Mmm, I don't know. Patches have to be maintained from version to version. If there are configure flags that allow us to do the same work, I would rather not maintain patches but use those options.