SRM: log client disconnecting at debug level

Currently, if a client disconnects during the SSL/GSI handshake then
the EOFException is logged as just EOFException.  This is both
non-obvious and unnecessary as dCache is behaving correctly.

This patch updates the message to be meaningful and reduces the
log-level to debug.
SRM: log client disconnecting at debug level

It is possible for the client to "give up" on a connection during the
SSL/GSI handshake exchange.  For example, this can happen if the
client doesn't trust the server's certificate.

When this happens, an EOFException is logged; for example:

30 Apr 2013 19:31:59 (SRM-zitpcx6184) [] java.io.EOFException

This message is both unintelligible and unnecessary, as dCache is
behaving correctly under the circumstances.

This patch updates the message to be meaningful, including the
client's IP address and port number in the diagnostic context. It also
reduces the log-level to debug.

Target: master
Request: 2.6
Patch: http://rb.dcache.org/r/5534/
Acked-by: Gerd Behrmann