Fix command quoting in CalledProcessError

CalledProcessError previously formatted cmd as `"... '%s' ..."`. This lead to
unbalanced quoting when cmd contains single-quotes or, more commonly, when cmd
is a list. This change updates the relevant format strings to use %r instead.

Author: Benjy Wiener

Lib/subprocess.py

@@ -145,13 +145,13 @@ def __init__(self, returncode, cmd, output=None, stderr=None):
     def __str__(self):
         if self.returncode and self.returncode < 0:
             try:
-                return "Command '%s' died with %r." % (
+                return "Command %r died with %r." % (
                         self.cmd, signal.Signals(-self.returncode))
             except ValueError:
-                return "Command '%s' died with unknown signal %d." % (
+                return "Command %r died with unknown signal %d." % (
                         self.cmd, -self.returncode)
         else:
-            return "Command '%s' returned non-zero exit status %d." % (
+            return "Command %r returned non-zero exit status %d." % (
                     self.cmd, self.returncode)
 
     @property