thread: Enrich and standardize disk usage logs
thread: Enrich and standardize disk usage logs

This modifies the sufficient log space message for threads from:
  Thread 1 disk space is sufficient: 11 > 10
  Thread 1 disk usage is high (packet path=/tmp/foobar): 10% < 10% free\n
to be:
  Thread 1 disk space is sufficient (packet path=/tmp/foobar): 11% free > 10% threshold
  Thread 1 disk usage is high (packet path=/tmp/foobar): 10% free <= 10% threshold
We also make minor additions to comments.

google/stenographer,google/stenographer,gconnell/stenographer,gconnell/stenographer,dcode/stenographer,dcode/stenographer,google/stenographer,gconnell/stenographer,dcode/stenographer