Add xenstore client

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

Signed-off-by: John Else <john.else@citrix.com>
Add generic plugin cleanup function

Signed-off-by: John Else <john.else@citrix.com>
Remove redundant handling of Sys.Break

It's already handled by the main loop.

Signed-off-by: John Else <john.else@citrix.com>
Add xenostats version of the main loop

This tries to talk to xenstore via the unix socket, so currently will
only work from dom0.

Signed-off-by: John Else <john.else@citrix.com>
Add runtime mode switch to dummy plugin

Signed-off-by: John Else <john.else@citrix.com>
Merge pull request #3 from johnelse/xenostats-prototype

Add initial xenostats frontend support