Sentinel: send SLAVEOF with MULTI, CLIENT KILL, CONFIG REWRITE.

This implements the new Sentinel-Client protocol for the Sentinel part:
now instances are reconfigured using a transaction that ensures that the
config is rewritten in the target instance, and that clients lose the
connection with the instance, in order to be forced to: ask Sentinel,
reconnect to the instance, and verify the instance role with the new
ROLE command.
Add SIGINT handler to cli --intrinsic-latency

If we run a long latency session and want to Ctrl-C out of it,
it's nice to still get the summary output at the end.
Merge pull request #1658 from mattsta/redis-cli-latency-clean-interrupt

Add SIGINT handler to cli --intrinsic-latency