opam: retrieve opam from $PATH with shutil.which

The default behavior of subprocess is to pull executables from a hardcoded list, which doesn't work when opam is installed manually in the user's home directory.

changed milestone to %Design and test next generation CI Automation [Roadmap - Tooling and infrastructure]

added activity::MRO label

assigned to @olasd

Jenkins job DLS/gitlab-builds #91 failed .
See Console Output and Coverage Report for more details.

@jenkins retry build kthxbye

@jenkins retry build

Jenkins job DLS/gitlab-builds #92 succeeded .
See Console Output and Coverage Report for more details.

approved this merge request

merged