Initial commit of guest RRD plugin

Signed-off-by: John Else <john.else@citrix.com>
Implement frontend of RRD plugin handshake

Signed-off-by: John Else <john.else@citrix.com>
Add some guest rrd plugin helper functions

Mostly copied from the perf-tools.hg repo.

Signed-off-by: John Else <john.else@citrix.com>
Write RRD data to the shared page

Signed-off-by: John Else <john.else@citrix.com>
Cleanup on SIGINT/SIGTERM

Signed-off-by: John Else <john.else@citrix.com>