FLUME-1920. Remove Hadoop dependency from integration tests

The file channel no longer actually depends on Hadoop, and this test was
exhibiting failures when Flume is built from paths containing the string
"hadoop". Since hadoop is not required for any of these tests, the
straightforward thing to do was to remove the now unnecessary Hadoop JAR
detection code completely.

(Li Xiang via Mike Percy)
Merge remote-tracking branch 'remotes/origin/trunk' into trunk