[SPARK-22583] First delegation token renewal time is not 75% of renewal time in Mesos

The first scheduled renewal time is is set to the exact expiration time,
and all subsequent renewal times are 75% of the renewal time. This makes
it so that the inital renewal time is also 75%.

## What changes were proposed in this pull request?

Set the initial renewal time to be 75% of renewal time.

## How was this patch tested?

Tested locally in a test HDFS cluster, checking various renewal times.

Author: Kalvin Chau <kalvin.chau@viasat.com>

Closes #19798 from kalvinnchau/fix-inital-renewal-time.