CA-314822: use scanLocked in should_prempt to avoid SR contents changing during scan
CA-314822: use scanLocked in should_prempt to avoid SR contents changing during scan

Signed-off-by: Mark Syms <655512b2a8f1aba6e4085462b623575da824f038@citrix.com>

xapi-project/sm,xapi-project/sm,xapi-project/sm