migrate to stestr

ostestr is no longer installed by default by infra and will be totally
removed longer term; stestr [1] is its replacement.

This is the reason out gate is failing with the following today:

nsx/tools/ostestr_compat_shim.sh: ostestr: not found

This patch moves us to stestr by:
- Updating tox.ini to use stestr rather than call ostestr_compat_shim.sh
and in turn ostestr.
- Removing ostestr_compat_shim.sh as its no longer used.

Change-Id: I1f97df69500058a7d330f7be5735a54c68f35559

.stestr.conf

@@ -0,0 +1,3 @@
+[DEFAULT]
+test_path=./vmware_nsxlib/tests/unit
+top_dir=./

tools/ostestr_compat_shim.sh

@@ -1,9 +0,0 @@
-#!/bin/sh
-
-# Copied from neutron/tools. Otherwise no units tests are found.
-# preserve old behavior of using an arg as a regex when '--' is not present
-case $@ in
-  (*--*) ostestr $@;;
-  ('') ostestr;;
-  (*) ostestr --regex "$@"
-esac

tox.ini

@@ -15,7 +15,8 @@ deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 whitelist_externals = sh
 commands =
-  {toxinidir}/tools/ostestr_compat_shim.sh {posargs}
+  stestr run {posargs}
+  stestr slowest
 # there is also secret magic in ostestr which lets you run in a fail only
 # mode. To do this define the TRACE_FAILONLY environmental variable.