Fix for config file probe matching when the uid is all digits.
Fix for config file probe matching when the uid is all digits.

- If the uid listed in a yaml config file is composed solely of digits
  then the yaml parser thinks it is an int, but we expect a string.
- Work around this by always converting the uid to string.

pyocd/pyOCD,flit/pyOCD,mbedmicro/pyOCD,pyocd/pyOCD,mesheven/pyOCD,mesheven/pyOCD,flit/pyOCD,mbedmicro/pyOCD,mesheven/pyOCD,mbedmicro/pyOCD