tools, scripts: refactor error-out statements of Python scripts

In Python, sys.exit() function can also take an object other
than an integer.

If an integer is given to the argument, Python exits with the return
code of it.  If a non-integer argument is given, Python outputs it
to stderr and exits with the return code of 1.

That means,

    print >> sys.stderr, "Blah Blah"
    sys.exit(1)

is equivalent to

    sys.exit("Blah Blah")

The latter is a useful shorthand.

Note:
Some error messages in Buildman and Patman were output to stdout.
But they should go to stderr.  They are also fixed by this commit.
This is a nice side effect.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Simon Glass <sjg@chromium.org>

scripts/mailmapper

@@ -59,8 +59,7 @@ MIN_COMMITS = 50
 try:
     toplevel = subprocess.check_output(['git', 'rev-parse', '--show-toplevel'])
 except subprocess.CalledProcessError:
-    print >> sys.stderr, 'Please run in a git repository.'
-    sys.exit(1)
+    sys.exit('Please run in a git repository.')
 
 # strip '\n'
 toplevel = toplevel.rstrip()