Change log level from ERROR to warn.

Change log level from ERROR to warn.

Description:
When a connection is termination by Peer, following log is logged at
error level causing to get captured in teardown making TC as failure.

Exception occurred while processing connection pipeline
io.netty.channel.unix.Errors$NativeIoException: readAddress(..) failed: Connection reset by peer

Change the log level from ERROR to warn as this exception is expected
during connection teardown and not making TC to mark as fail for this.

JIRA : OVSDB-496

Signed-off-by: Chetan Arakere Gowdru <chetan.arakere@altencalsoftlabs.com>
Change-Id: I82a585d4478f07e29f8b04600b7df95bb98c6d08
Signed-off-by: Chetan Arakere Gowdru <chetan.arakere@altencalsoftlabs.com>