daemon: Fix xfs_info parser because of new format.

The old parser had several problems: firstly it called the error path
sometimes without calling reply_with_error causing a protocol hang.
More seriously it had hard-coded line numbers, and since Fedora 21 the
output of xfs_info has changed, moving lines around.

Change the parser to be more robust against added fields by using the
first name on the line as the section name, thus 'bsize=' is
interpreted differently depending on whether it appears in the "data"
section or the "naming" section.

Ensure also that we don't call the error path without calling
reply_with_error, which is a side-effect of the above change.