Blacklist 'caches' for ts_mon.
Blacklist 'caches' for ts_mon.

This makes internal dashboard unusable since the 'caches' value space is
unbounded.

R=vadimsh@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2950883003

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py