Description:
============
If you have a relay log index file that has ended up with
some relay log files that do not exists, then RESET SLAVE
ALL is not enough to get back to a clean state.

Analysis:
=========
In the bug scenario slave server is in stopped state and
some of the relay logs got deleted but the relay log index
file is not updated.

During slave server restart replication initialization fails
as some of the required relay logs are missing. User
executes RESET SLAVE/RESET SLAVE ALL command to start a
clean slave. As per the documentation RESET SLAVE command
clears the master info and relay log info repositories,
deletes all the relay log files, and starts a new relay log
file. But in a scenario where the slave server's
Relay_log_info object is not initialized slave will not
purge the existing relay logs. Hence the index file still
remains in a bad state. Users will not be able to start
the slave unless these files are cleared.

Fix:
===
RESET SLAVE/RESET SLAVE ALL commands should do the cleanup
even in a scenario where Relay_log_info object
initialization failed.

Backported a flag named 'error_on_rli_init_info' which is
required to identify slave's Relay_log_info object
initialization failure. This flag exists in MySQL-5.6
onwards as part of BUG#14021292 fix.

During RESET SLAVE/RESET SLAVE ALL execution this flag
indicates the Relay_log_info initialization failure.
In such a case open the relay log index/relay log files
and do the required clean up.