libxl: create domain 'error' node in xenstore
Several PV drivers (both historically and currently [1]) report errors
by writing text into /local/domain/$DOMID/error. This patch creates the
node in libxl and makes it writable by the domain, and also adds some
text into xenstore-paths.pandoc to state what the node is for.
[1] https://xenbits.xen.org/gitweb/?p=pvdrivers/win/xenvif.git;a=blob;f=src/xenvif/frontend.c;hb=HEAD#l459
Signed-off-by: Paul Durrant <paul@xen.org>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>