use run_shell_cmd in custom easyblock for Qt

[branfosj]

(created using eb --new-pr)

[branfosj]

Test report by @branfosj

Overview of tested easyconfigs (in order)

• SUCCESS Qt5-5.14.2-GCCcore-10.2.0.eb
• SUCCESS Qt5-5.15.2-GCCcore-10.3.0.eb
• SUCCESS double-conversion-3.3.0-GCCcore-13.2.0.eb
• SUCCESS libGLU-9.0.3-GCCcore-13.2.0.eb
• SUCCESS snappy-1.1.10-GCCcore-13.2.0.eb
• SUCCESS Qt5-5.15.13-GCCcore-13.2.0.eb

Build succeeded for 6 out of 6 (3 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/c668344c3ad09af608acbe47dbc65ee3 for a full test report.

[boegel]

lgtm

[boegel]

Test report by @boegel

Overview of tested easyconfigs (in order)

• SUCCESS Qt5-5.15.13-GCCcore-13.2.0.eb

Build succeeded for 1 out of 1 (1 easyconfigs in total)
node3564.doduo.os - Linux RHEL 8.8, x86_64, AMD EPYC 7552 48-Core Processor, Python 3.6.8
See https://gist.github.com/boegel/8e510425f9cea3c0b74200d44cdec584 for a full test report.