HPCC-8909 Throw error if Thor slaves and master have different build versions

Code was already in place for this, but was not giving any warning in debug
builds.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #4132 from richardkchapman/thor-mismatch

HPCC-8909 Throw error if Thor slaves and master have different build versions

Reviewed-By: Jake Smith <jake.smith@lexisnexis.com>