Replace sed with python script

sed escaping is wrong: e.g. re.escape() will escape `+`, but with BRE escaped 
plus is quantifier

tests/test_shells/postproc.py

@@ -0,0 +1,32 @@
+#!/usr/bin/env python
+
+from __future__ import unicode_literals
+
+import os
+import socket
+import sys
+import codecs
+
+
+fname = sys.argv[1]
+new_fname = fname + '.new'
+pid_fname = 'tests/shell/3rd/pid'
+
+with open(pid_fname, 'r') as P:
+	pid = P.read().strip()
+hostname = socket.gethostname()
+user = os.environ['USER']
+
+with codecs.open(fname, 'r', encoding='utf-8') as R:
+	with codecs.open(new_fname, 'w', encoding='utf-8') as W:
+		found_cd = False
+		for line in R:
+			if not found_cd:
+				found_cd = ('cd tests/shell/3rd' in line)
+				continue
+			line = line.replace(pid, 'PID')
+			line = line.replace(hostname, 'HOSTNAME')
+			line = line.replace(user, 'USER')
+			W.write(line)
+
+os.rename(new_fname, fname)

tests/test_shells/test.sh

@@ -24,12 +24,8 @@ run_test() {
 	while screen -S "$SESNAME" -X blankerprg "" > /dev/null ; do
 		sleep 1s
 	done
-	sed -i -e "1,3 d" \
-	       -e s/$(cat tests/shell/3rd/pid)/PID/g \
-	       -e "s/$(python -c 'import re, socket; print (re.escape(socket.gethostname()))')/HOSTNAME/g" \
-	       -e "s/$(python -c 'import os, re; print (re.escape(os.environ["USER"]))')/USER/g" \
-	       tests/shell/screen.log
-	if ! diff -u tests/test_shells/${SH}.ok tests/shell/screen.log ; then
+	./tests/test_shells/postproc.py tests/shell/screen.log
+	if ! diff -u tests/test_shells/${SH}.ok tests/shell/screen.log | cat -v ; then
 		return 1
 	fi
 	return 0

tests/test_shells/zsh.ok

@@ -1,3 +1,4 @@
+
 
 USER  ⋯  tests  shell  3rd  POWERLINE_COMMAND=( $POWERLINE_COMMAND -c ext.shell.theme=default_leftonly )
 
 USER   BRANCH  ⋯  tests  shell  3rd  cd .git
 
 USER   BRANCH  ⋯  shell  3rd  .git  cd ..