packaging: don't use plain 'python' if another python has been specified
Before this change, packaging on CentOS 8 failed because 'python'
is used instead of 'python3'.
Change was tested with:
- make docker-centos7
- make docker-centos8
- make docker-ubuntu-bionic
Differential Revision: https://phab.mercurial-scm.org/D9464
#require clang-format test-repo
$ . "$TESTDIR/helpers-testrepo.sh"
$ cd "$TESTDIR"/..
$ for f in `testrepohg files 'set:(**.c or **.cc or **.h) and not "listfile:contrib/clang-format-ignorelist"'` ; do
> clang-format --style file $f > $f.formatted
> cmp $f $f.formatted || diff -u $f $f.formatted
> rm $f.formatted
> done