TESTS: Fix READ6 test

Commit 45a3752d163a2348918690084405293c62f5eebb skips all tests from
read-at-eol onwards when the LUN is large. Fix this by only skipping the
read-at-eol tests in this scenario.

Signed-off-by: Sitsofe Wheeler <sitsofe@yahoo.com>
Merge pull request #77 from sitsofe/read6

TESTS: Fix READ6 test