Improve DismanPing error message

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When you can't write, improve the error message:

{{{
DismanPing: old probe for rtra/equinix is probably running: Received SNMP 
response with error 
code
  error status: notWritable
  index 1 (OID: 
1.3.6.1.2.1.80.1.2.1.23.9.115.109.111.107.101.112.105.110.103.12.114.116.114.97.
47.101.11
3.117.105.110.105.120)
SNMPv2c_Session (remote host: "rtra.ietf69.org" [130.129.1.2].161)
                   community: "pinger"
                  request ID: -731840551
                 PDU bufsize: 8000 bytes
                     timeout: 1s
                     retries: 2
                     backoff: 1)
}}}

Original issue reported on code.google.com by fen...@gmail.com on 20 Jul 2007 at 3:43