Use utils.exit rather than print+sys.exit

This replaces the use of a pattern along the lines of

    print(error message)
    sys.exit(1)

in a couple of place in the shell. utils.exit does much the same job,
but outputs to stderr.

Change-Id: I1d3b52e0685772c10aa806a8f208eb6dd7a0e7ef

glanceclient/shell.py

@@ -697,8 +697,6 @@ def main():
     try:
         OpenStackImagesShell().main(map(encodeutils.safe_decode, sys.argv[1:]))
     except KeyboardInterrupt:
-        print('... terminating glance client', file=sys.stderr)
-        sys.exit(1)
+        utils.exit('... terminating glance client')
     except Exception as e:
-        print(utils.exception_to_str(e), file=sys.stderr)
-        sys.exit(1)
+        utils.exit(utils.exception_to_str(e))