TLS + Kerberos Support in Accumulo

**Is your feature request related to a problem? Please describe.**
Both TLS and Kerberos can be configured and turned on at the zookeeper and hadoop layer. However, Accumulo is required to turn only one of them: SSL or SASL for Kerberos. Turning off SSL but still keeping the zookeeeper.ssl* JVM switches (so that Accumulo may connect to secured zookeepers) would not work with the following error. Two ACL entries were added: one for host certificate used during SSL connection, one for accumulo admin account (in kerberos) given to 'accumulo init' process.

```
2021-03-25T22:07:19,495 [manager.Manager] INFO : Starting delegation-token key manager
2021-03-25T22:07:19,500 [delegation.ZooAuthenticationKeyDistributor] ERROR: Saw more than one ACL on the node
2021-03-25T22:07:19,503 [delegation.ZooAuthenticationKeyDistributor] ERROR: Expected /accumulo/74df60b2-7f63-4306-8f82-f08a81ba2a33/delegation_token_keys to have ACLs [31,s{'auth,'}
] but was [31,s{'x509,'CN=accucluster3-0.domain}
, 31,s{'digest,'accumulo:KBeh49allLP6OCuJmbGiQ7Q0guQ=}
]
2021-03-25T22:07:19,501 [conf.SiteConfiguration] INFO : Found Accumulo configuration on classpath at /opt/muchos/install/accumulo-2.1.0-SNAPSHOT/conf/accumulo.properties
2021-03-25T22:07:19,505 [start.Main] ERROR: Thread 'manager' died.
java.lang.IllegalStateException: Delegation token secret key node in ZooKeeper is not protected.
at org.apache.accumulo.server.security.delegation.ZooAuthenticationKeyDistributor.initialize(ZooAuthenticationKeyDistributor.java:86) ~[accumulo-server-base-2.1.0-SNAPSHOT.jar:2.1.0-SNAPSHOT]
at org.apache.accumulo.manager.Manager.run(Manager.java:1154) ~[accumulo-manager-2.1.0-SNAPSHOT.jar:2.1.0-SNAPSHOT]
at java.lang.Thread.run(Thread.java:834) [?:?]
```

**Describe the solution you'd like**
Accumulo may be configured with both TLS + Kerberos on and connect to TLS + Kerberos enabled zookeeper and hadoop.

**Describe alternatives you've considered**
There is no alternative if TLS and Kerberos is enabled in zookeepers.

**Additional context**
Add any other context or screenshots about the feature request here.

Start by reading ZooAuthenticationKeyDistributor.java at initialize(), then trace the Manager.run() startup path and the ZooKeeper ACL handling shown in the stack trace. Reproduce the TLS-and-Kerberos configuration and verify that Accumulo can connect to secured ZooKeeper and Hadoop while the delegation-token key node accepts the resulting ACLs.

Written by the indexing model from the issue text.