BUG#39325 Server crash inside MYSQL_LOG::purge_first_log halts replicaiton

The patch reverses the order of the purging and updating events for log and
relay-log.info/index files respectively.

This solves the problem of having holes caused by crashes happening between updating
info/index files and purging logs.

This patch also contains an aditional test case for testing the crashing before purge logs.
      
NOTE1: This is a combined patch for BUG#38826 and BUG#39325. This patch is based on
bugteam tree and takes into account reviewers suggestions.

NOTE2: Merge from 5.0-bugteam