Modify threshold for persistent disk and cpu alerts to reduce noise

[cweibel]

Changes proposed in this pull request:

• Bump persistent disk alerts to closer to default, default is 90. The logsearch deployments will allow the data nodes to scale to 85% before preventing new shards from being placed. One of the nodes is at 85% as reported by curl -s 'localhost:9200/_cat/allocation?v' but prometheus sees the disk at 81%. So setting the prometheus alert threshold to 85% will silence the perfectly healthy logsearch data nodes with a couple percent to spare.
• Bumping the high cpu warnings (seen mostly on diego cells) from the default of 10m to 30m since there basically isn't anything we can do or would do as a result of this warning.
• Left the ephemeral disk alerts alone, the only one I found was from when I really did fill a disk on an emptvm, so these aren't noisy

Security considerations

Trying to reduce the noise so real issues are better seen.