CP-2190 for PR-1221: SR alerts for hosts can be configured on the SR now.

To reduce the effort of configuration, whereas previously it was
necessary to configure throughput alerts for an SR on each host
individually, now it is possible to set up a per-host SR throughput
alert for each host connected to an SR by writing to the SR's
other-config:perfmon key.
Merge pull request #1024 from thomassa/clearwater-pr1221

CP-2190 for PR-1221: SR alerts for hosts can be configured on the SR now.