xmppophone #7148427 Don't use error log for ejabberd connection [in-progress]

Ejabberd Connection may fail if unable to respond, for example,
if you request vcard of a user without any vcard.
This doesn't mean there is an error, so "warning" log is better.

appeared in<not specified>
done in1.0
closed by<not specified>
patch[log] use warning instead of error log level for ejabberd connection [in-progress]