Config to trigger broker shutdown/restart based on log delays

In addition to org.apache.activemq.store.kahadb.LOG_SLOW_ACCESS_TIME add the following for a sliding window to shutdown/restart the Broker on log timeouts:

WINDOW_SIZE --> Could be used to specify time in s/m
NUM_SLOW_ACCESSES_PER_WINDOW --> Determines number of occurrences
SLOW_ACCESS_SHUTDOWN_TIMEOUT --> Determines the time threshold beyond which accesses are considered slow.

Shutdown the broker if disk access times are over SLOW_ACCESS_SHUTDOWN_TIMEOUT a number of times (NUM_SLOW_ACCESSES_PER_WINDOW) over a WINDOW_SIZE window