Detect Python executable in Makefile

[ssbarnea]

make help failed on modern platforms that have only
python3 executable installed.

Signed-off-by: Sorin Sbarnea ssbarnea@redhat.com

[openshift-ci-robot]

Hi @ssbarnea. Thanks for your PR.

I'm waiting for a containers member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[giuseppe]

/ok-to-test

LGTM

[rhatdan]

/approve
/lgtm
Thanks @ssbarnea

[openshift-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: rhatdan, ssbarnea

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