Revert "[Makefile] Switch to python3."

This reverts commit 8d4babc9.
6 jobs for devel in 15 minutes and 44 seconds (queued for 1 second)
Status Name Job ID Coverage
  Build
failed devel-16.04-build #79689
allowed to fail

00:15:44

failed devel-18.04-build #79688

00:08:54

 
  Test
skipped devel-16.04-test #79691
allowed to fail
skipped devel-18.04-test #79690
allowed to fail
 
  Deploy
skipped devel-16.04-doc #79693
allowed to fail
skipped devel-18.04-doc #79692
allowed to fail
 
Name Stage Failure
failed
devel-16.04-build Build
make: *** [test-ci] Error 2
Running after_script
Running after script...
$ mv $DEVEL_HPP_DIR $CI_PROJECT_DIR
Uploading artifacts for failed job
Uploading artifacts...
workspace: found 16793 matching files

Uploading artifacts to coordinator... ok
id=79689 responseStatus=201 Created token=NxUYLFtr
ERROR: Job failed: exit code 1
failed
devel-18.04-build Build
make: *** [test-ci] Error 2
Running after_script
Running after script...
$ mv $DEVEL_HPP_DIR $CI_PROJECT_DIR
Uploading artifacts for failed job
Uploading artifacts...
workspace: found 6522 matching files

Uploading artifacts to coordinator... ok
id=79688 responseStatus=201 Created token=qsY_YnVY
ERROR: Job failed: exit code 1