Use the proper sys.path in build/print_python_deps.py

We need to ensure the main module's directory is the first entry in
sys.path.

BUG=662258

Review-Url: https://codereview.chromium.org/2489393002
Cr-Commit-Position: refs/heads/master@{#431327}

build/print_python_deps.py

@@ -82,7 +82,9 @@ def main():
                       help='Recursively include all non-test python files '
                       'within this directory. May be specified multiple times.')
   options = parser.parse_args()
-  sys.path.append(os.path.dirname(options.module))
+  # Replace the path entry for print_python_deps.py with the one for the given
+  # module.
+  sys.path[0] = os.path.dirname(options.module)
   imp.load_source('NAME', options.module)
 
   paths_set = _ComputePythonDependencies()