Fixed results output summary.
General tidy up of long lines.
Added a new field to json file, target_list, to allow the user to
override the set of targets used for the compilation.
Replace use of print and write with logging (with different levels).
Add the ability to choose the logging level on the command line.
Fix the exclusion of uARM from compilation.
Remove print_on_fail from run_cmd() functions, now use logging.
Usage: python tools/check_release.py
Run from the mbed-os directory.
For details on how the script works and how to set up the configuration
json file, please see the python file header.