dtest takes error level log as serious error. It is not a serious error
for streaming to fail to send a verb and fail a streaming session, for
example, the peer node is gone or stopped. Switch to use log level warn
instead of level error.
Fixes repair_additional_test.py:RepairAdditionalTest.repair_kill_3_test
Fixes: #1335
Message-Id: <0149d30044e6e4d80732f1a20cd20593de489fc8.1465979288.git.asias@scylladb.com>
(cherry picked from commit 94c9211b0e)
da77b8885f