update_payload: Fix most of lint styling issues.

This patch fixes a lot of pylint issues in the update_engine scripts. Majority
of this changes are based on recommendation found in:
	https://www.chromium.org/chromium-os/python-style-guidelines

It is a good idea to do these changes now, because if there are many pylint
errors when performing 'repo upload', serious problems can be overshadowed by a
lot of noise and eventually cause problems.

These fixes include:
	- Fixing executable shebangs to /usr/bin/python2.
	- Fixing import-error problems by disabiling them.
	- Removing pylint disables that are not valid anymore.
	- Changing all imports to proper absolute import format.
	- Change the import of PayloadError from update_payload.PayloadError for
	  simplicity.
	- Add pydoc strings for functions and classes that were missing.

The remaining unchanged pylint problmes include:

	- The header files of these scripts are in CrOS copyright format, but the
      the cros lint hook is configured to AoSP copyright format.
	- The test* functions in unittests are not compatible with CamelCase format.

BUG=chromium:796338
TEST=unittests pass
TEST=start_devserver
TEST=cros flash
TEST=scripts/paycheck.py

Change-Id: I7eed4d1625eb7c510c7949fada120de5a6a26c7b
Reviewed-on: https://chromium-review.googlesource.com/834875
Commit-Ready: Amin Hassani <ahassani@chromium.org>
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Sen Jiang <senj@chromium.org>

1 files changed, 5 insertions, 9 deletions

diff --git a/scripts/update_payload/checker.py b/scripts/update_payload/checker.py
index c710c47b..e4cb845f 100644
--- a/scripts/update_payload/checker.py
+++ b/scripts/update_payload/checker.py
@@ -21,11 +21,11 @@ import itertools
 import os
 import subprocess
 
-import common
-import error
-import format_utils
-import histogram
-import update_metadata_pb2
+from update_payload import common
+from update_payload import error
+from update_payload import format_utils
+from update_payload import histogram
+from update_payload import update_metadata_pb2
 
 
 #
@@ -970,8 +970,6 @@ class PayloadChecker(object):
             op_name)
 
       # Check: Hash verifies correctly.
-      # pylint cannot find the method in hashlib, for some reason.
-      # pylint: disable=E1101
       actual_hash = hashlib.sha256(self.payload.ReadDataBlob(data_offset,
                                                              data_length))
       if op.data_sha256_hash != actual_hash.digest():
@@ -1168,8 +1166,6 @@ class PayloadChecker(object):
     report.AddSection('signatures')
 
     # Check: At least one signature present.
-    # pylint cannot see through the protobuf object, it seems.
-    # pylint: disable=E1101
     if not sigs.signatures:
       raise error.PayloadError('Signature block is empty.')