Add validation that 'sudo' works for a given user inside of the agitator scripts

Original Jira ticket: https://issues.apache.org/jira/browse/ACCUMULO-1982

Main snippet:

```
It would be nice if we tested that sudoing to the desired user worked
for the current user and gave better error messages in the case of failure.
```

The code here has changed significantly since the original ticket was created so it is possible the need for this has lessened but from my quick investigation I did not find any validation checks.

Start by locating the agitator scripts and reviewing how they currently run commands as the desired user. Confirm the expected sudo check and error behavior with the original Jira ticket, then verify that failures clearly identify the problem and successful checks do not disrupt the scripts.

Written by the indexing model from the issue text.