xenstore: make memory report available via XS_CONTROL

xenstore: make memory report available via XS_CONTROL

Add a XS_CONTROL command to xenstored for doing a talloc report to a
file. Right now this is supported by specifying a command line option
when starting xenstored and sending a signal to the daemon to trigger
the report.

To dump the report to the standard log file call:

xenstore-control memreport

To dump the report to a new file call:

xenstore-control memreport <file>

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>