update custom easyblock for QuantumESPRESSO to be aware of MPI tests being disabled in EasyBuild configuration

[Crivella]

QE if compiled with MPI enabled will always run tests using the found mpicommand:

• Always true for the CMake version
• Can be avoided in the Makefile version but it is getting deprecated

This PR ensures the test-suite is skipped if --disable-mpi-tests tests is used.

[branfosj]

Test report by @branfosj

Overview of tested easyconfigs (in order)

• SUCCESS libxc-6.2.2-intel-compilers-2023.1.0.eb
• SUCCESS impi-2021.9.0-intel-compilers-2023.1.0.eb
• SUCCESS iimpi-2023a.eb
• SUCCESS HDF5-1.14.0-iimpi-2023a.eb
• SUCCESS imkl-2023.1.0.eb
• SUCCESS imkl-FFTW-2023.1.0-iimpi-2023a.eb
• SUCCESS intel-2023a.eb
• SUCCESS ELPA-2023.05.001-intel-2023a.eb
• SUCCESS QuantumESPRESSO-7.3-intel-2023a.eb

Build succeeded for 9 out of 9 (1 easyconfigs in total)
bear-pg0105u03a - Linux RHEL 8.6, x86_64, Intel(R) Xeon(R) Platinum 8360Y CPU @ 2.40GHz (icelake), Python 3.6.8
See https://gist.github.com/branfosj/5221ff8110f84de9748fc297bcd26ea1 for a full test report.

[branfosj]

Going in, thanks @Crivella!

[branfosj]

Test report by @branfosj

Overview of tested easyconfigs (in order)

• SUCCESS ELPA-2023.05.001-foss-2023a.eb
• SUCCESS libxc-6.2.2-GCC-12.3.0.eb
• SUCCESS QuantumESPRESSO-7.3-foss-2023a.eb

Build succeeded for 3 out of 3 (1 easyconfigs in total)
bear-pg0105u03a - Linux RHEL 8.6, x86_64, Intel(R) Xeon(R) Platinum 8360Y CPU @ 2.40GHz (icelake), Python 3.6.8
See https://gist.github.com/branfosj/1616e16f9934aaba8980289c85435401 for a full test report.