Not all devices have enough heap to fit a simulated heap block device,
however using a simulated heap block device is preferred if available
(reduced flash wear, faster testing).
Added MBED_TEST_SIM_BLOCKDEVICE for tests that only need a simulated
block device (wear_leveling + resilience), and added support for targets
that are known to have enough heap.
Changing this to none as result of build failures. Wifi needs own configuration
per an enviroment. By setting this to none, net tests are skipped for Realtek
platform.
Tools will figure out if user passed in a custom path (to indicate configration file for module) or whether they used a keyword (to indicate they'd like to use an mbed OS configuration)