A UDP request to the NIST servers can fail to return data due to UDP
packet loss. Since packets are not guaranteed with UDP, this is a valid
failure and should not be treated as a test failure. The test should retry
the request in this case. This commit adds those retries.
Having the echo tests generate any random character
caused issues serializing the test output into an
xml file. This change limits the characters generated
by the device to '0' - '9'.