Remove usage of env from Makefile rules

One of the benefits here of setting `SHELL := bash` is that we no longer
need to use env to set environment variables before a shell command.
Bash just handles that itself.

Removed a useless use of `cat`.

Dropped the `-e` from `bash -ex` as that is handled in
./openqa-label-known-issues-multi itsef.

I'm not completely sure about that `grep -v` but it seem like it was
trying to avoid the error from invalid JSON (noted in the comment).
Putting `-` prefix on a rule command tells `make` not to stop if the
command fails. Not sure that is correct here or not.

Makefile

@@ -28,10 +28,10 @@ test-python:
 	py.test tests)
 
 test-online:
-	cat ./tests/incompletes | env dry_run=1 bash -ex ./openqa-label-known-issues-multi
-	env dry_run=1 ./trigger-openqa_in_openqa
+	dry_run=1 bash -x ./openqa-label-known-issues-multi < ./tests/incompletes
+	dry_run=1 ./trigger-openqa_in_openqa
 	# Invalid JSON causes the job to abort with an error
-	env tw_openqa_host=example.com dry_run=1 ./trigger-openqa_in_openqa | grep -v 'parse error:'
+	-tw_openqa_host=example.com dry_run=1 ./trigger-openqa_in_openqa
 
 checkstyle: test-shellcheck test-yaml