TestClusters: convert kerberos-tests (#43232)
TestClusters: convert kerberos-tests (#43232)

Looks like cluster formation tasks no longer plays nice wit
test.fixtures so we just convert this to use testclusters.
HonzaKral/elasticsearch,scorpionvicky/elasticsearch,nknize/elasticsearch,HonzaKral/elasticsearch,coding0011/elasticsearch,gingerwizard/elasticsearch,scorpionvicky/elasticsearch,gingerwizard/elasticsearch,scorpionvicky/elasticsearch,robin13/elasticsearch,HonzaKral/elasticsearch,robin13/elasticsearch,GlenRSmith/elasticsearch,nknize/elasticsearch,nknize/elasticsearch,HonzaKral/elasticsearch,GlenRSmith/elasticsearch,GlenRSmith/elasticsearch,gingerwizard/elasticsearch,uschindler/elasticsearch,GlenRSmith/elasticsearch,uschindler/elasticsearch,coding0011/elasticsearch,uschindler/elasticsearch,robin13/elasticsearch,gingerwizard/elasticsearch,GlenRSmith/elasticsearch,uschindler/elasticsearch,nknize/elasticsearch,robin13/elasticsearch,gingerwizard/elasticsearch,gingerwizard/elasticsearch,scorpionvicky/elasticsearch,scorpionvicky/elasticsearch,uschindler/elasticsearch,coding0011/elasticsearch,coding0011/elasticsearch,robin13/elasticsearch,gingerwizard/elasticsearch,nknize/elasticsearch,coding0011/elasticsearch