utility to wrap the mbed test loader for use by yotta targets

 mbed-test-wrapper is used to wrap the mbed test loader, so that it can
 be used by yotta targets to run tests on target embedded hardware platforms
 (e.g. K64F).
 .
 The executable file to be tested on the desired target hardware is first
 converted to a .bin file if necessary (via arm-none-eabi-objcopy), and then
 executed via mbedhtrun using the configured mount point, serial port and
 yotta target name.