replace run_cmd with run_shell_cmd in custom easyblock for TINKER (tinker.py)

[branfosj]

(created using eb --new-pr)

[branfosj]

Test report by @branfosj

Overview of tested easyconfigs (in order)

• FAIL (build issue) TINKER-8.8.1-foss-2020a.eb (partial log available at https://gist.github.com/branfosj/0bfa4e8fcbebf6bfdd1512d86de42387)

Build succeeded for 0 out of 1 (1 easyconfigs in total)
bear-pg0211u08b.bear.cluster - Linux RHEL 8.6, x86_64, Intel(R) Xeon(R) Gold 6248 CPU @ 2.50GHz (cascadelake), Python 3.6.8
See https://gist.github.com/branfosj/efd536c279f8d0f015f3f1d5a2e3fc8f for a full test report.

edit failure due to source not being available

[branfosj]

Test report by @branfosj

Overview of tested easyconfigs (in order)

• SUCCESS TINKER-8.8.3-foss-2020a.eb

Build succeeded for 1 out of 1 (1 easyconfigs in total)
bear-pg0211u08b.bear.cluster - Linux RHEL 8.6, x86_64, Intel(R) Xeon(R) Gold 6248 CPU @ 2.50GHz (cascadelake), Python 3.6.8
See https://gist.github.com/branfosj/49f205aebc32eb87be8788fce26316d1 for a full test report.

[bartoldeman]

LGTM