BT LE test case platform support enhancement

The qtconnectivity's bluetooth module has a Bluetooth Low Energy (BT LE) test case where one device runs a BT LE server ("bluetoothtestdevice") and the other end runs a BT LE client ("tst_qlowenergycontroller_device") which is the actual Qt test case.

The test-case has been verified with Linux-client => Android-server to pass.

This Jira task is about testing, documenting and improving the other platform test combinations:
1) test the platform combinations
2) enhance test robustness where needed and possible
3) document limitations and exceptions to the test case
4) file actual bluetooth bugs if found

If there are major bugs or findings in some platform, fixing them is not in the scope of this task. Trivial things can be addressed.

The fundamental goal with this task is to make BT LE testing easier, which will help in verifying new features and adding test cases for them.