Remove superfluous text from fail_msg
Remove superfluous text from fail_msg

Phrase "Please refer to OSTF logs for more details." is superfluous
in fail_msg, because such kind of text is appended to an error message
by method verify_response_true() in case of test failure.

Change-Id: I4f772d68e85c79c7e2cf1a2b8b4059f252f22ef7
Closes-Bug: #1515251

stackforge/fuel-ostf,stackforge/fuel-ostf