Remove --test-path option from stestr run

The .stestr.conf already defines the test path
so we don't need to specify it on the command line.

Change-Id: I66892fa0b17895207307bc15b5ef8b322a7a010e

tox.ini

@@ -17,7 +17,8 @@ deps =
 whitelist_externals =
   rm
 commands = rm -f .testrepository/times.dbm
-           stestr --test-path=./watcherclient/tests/unit run {posargs}
+           # The --test-path is defined in .stestr.conf
+           stestr run {posargs}
            stestr slowest
 
 [testenv:pep8]