Use python2

scripts/gen_ir.py uses "#!/usr/bin/env python"
1 job for gitlab-ci-testing in 17 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
failed #10514
test

00:00:17

 
Name Stage Failure
failed
test Test There is an unknown failure, please try again
Get:21 http://archive.ubuntu.com/ubuntu xenial-security/universe amd64 Packages [117 kB]
Fetched 25.0 MB in 6s (3644 kB/s)
Reading package lists...
$ apt-get -y install gcc make python2 perl git
Reading package lists...
Building dependency tree...
Reading state information...
E: Unable to locate package python2
ERROR: Job failed: exit code 1