Add pylint to presubmit checks

drover.py

Index: drover.py
diff --git a/drover.py b/drover.py
index 77922cd705790ca75d2bad7bf129ad629c63c795..9329fda2b6611781c79fafe97813d25e6d80181b 100755
--- a/drover.py
+++ b/drover.py
@@ -402,11 +402,9 @@ def drover(options, args):
   # Override the default properties if there is a drover.properties file.
   global file_pattern_
   if os.path.exists("drover.properties"):
-    f = open("drover.properties")
-    exec(f)
-    f.close()
-    if FILE_PATTERN:
-      file_pattern_ = FILE_PATTERN
+    FILE_PATTERN = file_pattern_
+    execfile("drover.properties")
+    file_pattern_ = FILE_PATTERN
 
   if options.revert and options.branch:
     url = BRANCH_URL.replace("$branch", options.branch)