tests: iperf3: Support testing parallel iperf3 clients in test

Since tests running a single MS and several of them are really similar,
generic code handling the test for N concurrent iperf3 sessions is
writen an moved to testlib, and existing and new test use that code.

Change-Id: I57799fde49e6845379cca332eec0a1f70aaecd2b
diff --git a/suites/gprs/iperf3m4.py b/suites/gprs/iperf3m4.py
new file mode 100755
index 0000000..1cc27ed
--- /dev/null
+++ b/suites/gprs/iperf3m4.py
@@ -0,0 +1,8 @@
+#!/usr/bin/env python3
+from osmo_gsm_tester.testenv import *
+
+import testlib
+suite.test_import_modules_register_for_cleanup(testlib)
+from testlib import setup_run_iperf3_test_parallel
+
+setup_run_iperf3_test_parallel(4)