Fix stestr command error in doc
This patch change "stestr run -n --load-list"
to "stestr run --load-list" in 242 line in
doc/source/contributor/testing.rst.
Closes-Bug:
@@ -239,4 +239,4 @@ Then run the unit test with pdb enabled:
# Or to get a list of tests to run
stestr list test_volume_utils > tests_to_run.txt
- stestr run -n --load-list tests_to_run.txt
+ stestr run --load-list tests_to_run.txt
