Fix buggy #! lines using "/usr/bin/env python2.7 -u".

The #! line processing interpreted the argument to pass to `env` as
"python2.7 -u", which obviously isn't a real program.

We fix this by setting the PYTHONUNBUFFERED environment variable
inside the program, which has the same effect.

Thanks to Dan Fedele for the bug report and suggested solution!

scripts/lib/unpack-zulip

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2.7 -u
+#!/usr/bin/env python2.7
 import os
 import sys
 import subprocess
@@ -6,6 +6,8 @@ import datetime
 import tempfile
 import glob
 
+os.environ["PYTHONUNBUFFERED"] = "y"
+
 sys.path.append(os.path.join(os.path.dirname(__file__), '..', ".."))
 from zulip_tools import DEPLOYMENTS_DIR, FAIL, ENDC, make_deploy_path
 

scripts/lib/upgrade-zulip

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2.7 -u
+#!/usr/bin/env python2.7
 import os
 import sys
 import subprocess
@@ -6,6 +6,8 @@ import logging
 import shutil
 import time
 
+os.environ["PYTHONUNBUFFERED"] = "y"
+
 sys.path.append(os.path.join(os.path.dirname(__file__), '..', '..'))
 from zulip_tools import DEPLOYMENTS_DIR, LOCK_DIR, FAIL, WARNING, ENDC, \
     su_to_zulip

scripts/lib/upgrade-zulip-stage-2

@@ -1,9 +1,11 @@
-#!/usr/bin/env python2.7 -u
+#!/usr/bin/env python2.7
 import subprocess
 import os
 import sys
 import logging
 
+os.environ["PYTHONUNBUFFERED"] = "y"
+
 sys.path.append(os.path.join(os.path.dirname(__file__), '..', '..'))
 from zulip_tools import FAIL, WARNING, ENDC, su_to_zulip
 

tools/test-backend

@@ -12,4 +12,5 @@ esac
 cd "$(dirname "$0")"/..
 ./tools/generate-fixtures
 # "-u" uses unbuffered IO, which is important when wrapping it in subprocess
-/usr/bin/env python2.7 -u ./manage.py test "$target" --settings=zproject.test_settings "$@"
+export PYTHONUNBUFFERED="y"
+/usr/bin/env python2.7 ./manage.py test "$target" --settings=zproject.test_settings "$@"

tools/update-deployment

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2.7 -u
+#!/usr/bin/env python2.7
 import os
 import sys
 import subprocess
@@ -7,6 +7,8 @@ import datetime
 import shutil
 import time
 
+os.environ["PYTHONUNBUFFERED"] = "y"
+
 sys.path.append(os.path.join(os.path.dirname(__file__), '..'))
 from zulip_tools import DEPLOYMENTS_DIR, LOCK_DIR, FAIL, WARNING, ENDC, make_deploy_path