Fix code that is causing a pylint error in drover.py.

drover.py

Index: drover.py
diff --git a/drover.py b/drover.py
index 77922cd705790ca75d2bad7bf129ad629c63c795..2f726a5d19fdc6b0a9c6f2022694bfdae7732c8e 100755
--- a/drover.py
+++ b/drover.py
@@ -402,9 +402,8 @@ 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()
+    FILE_PATTERN = file_pattern_
+    execfile("drover.properties")
     if FILE_PATTERN:
       file_pattern_ = FILE_PATTERN