ENG-6734: Move voltdb_testprocs from tests/frontend/ to
tests/testprocs, where it can be built and included separately in the
classpath for all the tests, and excluded from LocalCluster's
out-of-process server classpath.  This forces any catalog dependencies
to be actually in the catalog instead of silently picked up from the
default classpath.
ENG-6734: Add a helpful comment
Merge pull request #1575 from VoltDB/eng6734

ENG-6734: move voltdb_testprocs.  r=jhugg