zdtm.py: Make print_sep shorter and print aligned lines

Current implementation of print_sep has off-by-one-like issue -- it
can print one character more :) Fix this and make the code shorter.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

test/zdtm.py

@@ -659,9 +659,7 @@ def self_checkskip(tname):
 	return False
 
 def print_sep(title, sep = "="):
-	sep_len = (80 - len(title) - 2) / 2
-	sep = sep * sep_len
-	print "%s %s %s" % (sep, title, sep)
+	print (" " + title + " ").center(80, sep)
 
 def grep_errors(fname):
 	print_sep("grep Error")