Use "#!/usr/bin/env python2.7" only in utilities

test/core/bad_client/gen_build_yaml.py

test/core/end2end/gen_build_yaml.py

test/core/httpcli/test_server.py

tools/buildgen/build-cleaner.py

tools/buildgen/mako_renderer.py

tools/distrib/check_copyright.py

tools/distrib/python/docgen.py

tools/distrib/python/submit.py

tools/profile_analyzer/profile_analyzer.py

tools/run_tests/antagonist.py

tools/run_tests/port_server.py

tools/run_tests/run_tests.py