DERBY-5133; nightly test failure in derbyall/storeall/storemore/SpaceTable
   addressing review input; using JDBCTestCase.dropTable(), simplifying the retry and eliminating the code duplication, and adjusting comments.
   Also addresses failure with Java8 because of different test case sequence.


git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1594451 13f79535-47bb-0310-9956-ffa450edef68