net_test_bluetooth: Improve set/get name logic

net_test_bluetooth: Improve set/get name logic

Without this CL semaphore_wait would instantly return due to the fact
that enabling the adapter would cause the properties callback to post
immediatly. Also prevented the test from returning a false positive if the
original device name was the same as the test name.

Change-Id: I987efcb9a5ef58209d37d2fc21f3c149fb3e556c