Fix broken sstableloader tests

Neither the exit status of the sstableloader subprocess
or the stress subprocess to read and validate the data were
checking exit statuses, so failures went unnoticed.  In particular,
the tests failed to catch CASSANDRA-6205.

This patch does the following:
 * Fixes incompressible_data_in_compressed_table_test, which seemed to
   be totally broken
 * Instead of using stress to insert and validate data (ccm doesn't
   check exit statuses for stress), a normal cursor is used.
 * The exit status of the sstableloader subprocess is checked
 * Cleanup of unused imports, bad whitespace, and other pep8 violations
Merge pull request #23 from thobbs/sstableloader-fixes

Fix broken sstableloader tests
Really disable vnodes, allow setting speculative_retry
Update INSTALL.md

Update docs to use java7
Add last_test_dir to .gitignore
Adds delete_insert_test from CASSANDRA-5510
Adds user types CQL tests
Remove forced version in delete_insert_test
Add test for 6330
Merge branch 'master' of github.com:riptano/cassandra-dtest
Test for #6327
large count test
Improve set test to detect 6341