UserGroupInformation TGT renewer refreshTime should be based on getNextTgtRenewalTime

The calculation of nextRefresh in UserGroupInformation#spawnAutoRenewalThreadForUserCreds is currently based on:

nextRefresh = Math.max(getRefreshTime(tgt),
              now + kerberosMinSecondsBeforeRelogin);

Most of the time nextRefresh = getRefreshTime(tgt). If it is renewing exactly on refreshTime, and there are parallel operations using expired ticket.
There is a time gap that some operations might not perform until the next tgt is obtained. Ideally, we want to keep service uninterrupted, therefore getNextTgtRenewalTime supposed to calculate the time a few minutes before Kerberos tgt expired to determine the nextRefresh time.
It looks like we are not using getNextTgtRenewalTime method to calculate nextRefresh instead opt-in to use ticket expiration time as base line for nextRefresh.

Kudos for eyang for reporting the issue originally in HADOOP-15593.