Integration with status reporter in wsrep-lib.
Status reporter reports changes in wsrep state and logged errors/
warnings to a json file which then can be read and interpreted by
an external monitoring tool.
Rationale: until the server is fully initialized it is unaccessible
by client and the only source of information is an error log which
is not machine-friendly. Since wsrep node can spend a very long time
in initialization phase (state transfer), it may be a very long time
that automatic tools can't easily monitor its liveness and progression.
New variable: wsrep_status_file specifies the output file name.
If not set, no file is created and no reporting is done.
Reviewed-by: Jan Lindström <jan.lindstrom@mariadb.com>
