bluetooth: New test based on daemonized l2test

This MR is a fix for [YT-193] EMC Bluetooth test: l2test based.

Reworked existing Bluetooth tests to use a daemon mode for l2test, in particular:

• updated a service script to launch l2test in daemon mode. In this mode it establishes a BT connection to remote with running test server and waits for signal to start a data transfer.
• reworked a wait script to check connections opened by l2test instead of checking a log file.
• updated a test script itself to switch from l2ping to l2test. Herewith it is possible to define a number of packages to transfer and delay between transfers as input arguments for this script. Also there is an argument to set the number of "good" packages which should be successfully received back to return "pass";
• updated corresponding runtest configuration files.

An MR which enables a daemon for l2test can be found here: seco-ne/yocto/layers/meta-seconorth-distro!811 (closed)