Fixed a minor glitch in each of sub_test and paratest.server
Followed up on Tom's reviewer comments.
Merge pull request #616 from vasslitvinov/minor-sub_test-paratest-fixes

Fixed a minor glitch in each of sub_test and paratest.server

* In sub_test, eliminate the confusion between $CHPL_HOME/test/users/USERNAME/... and /users/USERNAME.

I suspect that the conditional that I eliminated was added so you can say "start test somedir/sometest.chpl" and have it test $CHPL_HOME/test/somedir/sometest.chpl even when you are not in $CHPL_HOME/test. If so, sub_test does not implement this consistently. I.e. for a few sometest.* files, PREDIFF, etc., sub_test looks them up in the current directory always. So I force the other files to be looked up in the current directory, too.

* For "paratest.server --show-all-errors", show each error just once. While there, streamlined the code.

Reviewed by Tom.