hdtest fix

Fix: hdtest should return teststatus when argument -e is set, but -e has no effect. Instead hdtests returns always 0 when the test run is done, regardless if the test revealed errors.

Feature-Add: In addition a new binary-mode is implemented, which writes the raw test results in memory, instead of a formatted string. This is to make it easier for the caller to process the results, as there is not need to parse a string.