Last contact for tablet server on monitor seemed incorrect

**Describe the bug**

Working with a handful of half dead tablet sever that were holding their locks in zookeeper but not accepting RPC request it seems the last contact times for these tablet servers was always within the last few seconds. However I do not think the manager was successfully contacting them. It is possible I made a mistake, want to try to reproduce this and opening this issue as a reminder.

**Versions (OS, Maven, Java, and others, as appropriate):**
- Affected version(s) of this project: 2.1.x

**Expected behavior**

The last contact time increases when tablet server can not be contacted.

Start by reproducing the report with tablet servers that hold ZooKeeper locks but do not accept RPC requests, then inspect how the manager records their last contact time. Confirm that the displayed time increases when a tablet server cannot be contacted; the issue does not name specific files or tests.

Written by the indexing model from the issue text.