lint: properly handle last line indentation

We fix two issues with the last triple quotes:
(1) We flagged blank lines at the end of docstrings for functions, but
    not for modules or classes.  We added the check to the function code
    instead of the common code.
(2) We didn't check the indentation of the trailing docstring at all.

We fix (1) by moving the test to the common line checking code.

By fixing (2), we're able to unify the one check that was specific to
functions with the common code.

BUG=None
TEST=`cros lint` catches a bunch of bad docstrings

Change-Id: I05642abd3475516bc340584e120324f36ff175d7
Reviewed-on: https://chromium-review.googlesource.com/387386
Reviewed-by: Allen Li <ayatane@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/cros_vm.py b/scripts/cros_vm.py
index b8b80f9..b32486b 100644
--- a/scripts/cros_vm.py
+++ b/scripts/cros_vm.py
@@ -2,9 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-"""Script for VM Management.
-
-"""
+"""Script for VM Management."""
 
 from __future__ import print_function