releasetools: Make scripts pylint clean.

Clean up the following scripts.
  blockimgdiff.py
  common.py
  edify_generator.py
  img_from_target_files.py
  ota_from_target_files.py

Seems we don't have a way to force pylint-ing the scripts using
per-directory pylintrc files (and we don't have pylint tool in AOSP
repo), per
https://android.googlesource.com/platform/tools/repohooks/#todo_limitations.

Test: `m dist`
Test: pylint --rcfile=pylintrc <script.py>
Change-Id: Ia6fd1ddc86f4d84c68e500f225d4a89d0fea8ec7
diff --git a/tools/releasetools/pylintrc b/tools/releasetools/pylintrc
index 7b3405c..2a30742 100644
--- a/tools/releasetools/pylintrc
+++ b/tools/releasetools/pylintrc
@@ -62,7 +62,7 @@
 # --enable=similarities". If you want to run only the classes checker, but have
 # no Warning level messages displayed, use"--disable=all --enable=classes
 # --disable=W"
-disable=invalid-name,missing-docstring,too-many-branches,too-many-locals,too-many-arguments,too-many-statements,duplicate-code,too-few-public-methods,too-many-instance-attributes,too-many-lines,too-many-public-methods,locally-disabled,fixme
+disable=invalid-name,missing-docstring,too-many-branches,too-many-locals,too-many-arguments,too-many-statements,duplicate-code,too-few-public-methods,too-many-instance-attributes,too-many-lines,too-many-public-methods,locally-disabled,fixme,not-callable
 
 
 [REPORTS]