Make setenv consistent for unit, func, and api-samples

Since ostestr switched to running stestr under the covers, we lost the
old magic setting of the environment variables via .testr.conf for
capturing stderr/stdout and the test timeout. This makes the unit,
functional, and api-samples envs consistent with the py27 env that was
already updated to set those variables.

This also updates the pretty_tox3.sh script to run stestr directly.

Change-Id: I27fa9b7e25c1a1dc921653eec84864423f898a85

tools/pretty_tox3.sh

@@ -9,7 +9,7 @@ else
 fi
 
 if [ -z "$TESTRARGS" ]; then
-    ostestr --blacklist_file $blacklist_file
+    stestr run --blacklist-file $blacklist_file
 else
-    ostestr -r "$TESTRARGS"
+    stestr run "$TESTRARGS"
 fi