Further workarounds for the broken string marshalling in xmlrpclib. Regardless

Further workarounds for the broken string marshalling in xmlrpclib.  Regardless
of the encoding used, one still may not include non-printable characters in an
XML document.  When a dmesg contains a ^D character, something seen on one of
our test machines, an invalid XML document is generated.

Use a trick by David Mertz to work around this -- escape the string using
Python's repr function.

Signed-off-by: Ewan Mellor <ewan@xensource.com>