Improve error reporting when commands fail

Previously we'd only return a single line from stderr when
a command fails. This made it hard to diagnose some SSH
failures which output a line of '*' as the first line of
stderr.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Fix comments command wrt change in OperationQuery constructor

The comments command relied on the 'patches' arg to OperationQuery
having a fixed position. This changed when the 'rawquery' arg was
added, so fix by using a named parameter instead.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>