block_perf: add a watchdog thread
block_perf: add a watchdog thread

Detect deadlocks and print an error. Periodically dump the state
of each event channel.

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@eu.citrix.com>

talex5/mirage-skeleton,haesbaert/mirage-skeleton,haesbaert/mirage-skeleton,sjfloat/mirage-skeleton,djs55/mirage-skeleton,nasrallahmounir/mirage-skeleton,sjfloat/mirage-skeleton,Drup/mirage-skeleton,infidel/mirage-skeleton,mattgray/mirage-skeleton,mattgray/mirage-skeleton,lnmx/mirage-skeleton,lnmx/mirage-skeleton,yomimono/mirage-skeleton,nasrallahmounir/mirage-skeleton,djs55/mirage-skeleton,samoht/mirage-skeleton,infidel/mirage-skeleton,mor1/mirage-skeleton,samoht/mirage-skeleton,mor1/mirage-skeleton,Drup/mirage-skeleton,yomimono/mirage-skeleton,mirage/mirage-skeleton,mirage/mirage-skeleton