'Wrong parameters to functi

START SLAVE reports vague error when it fails to register on master:
"Wrong parameters to function register_slave".

If master failed to register slave because of too long
'report-host'/'report-user'/'report-password', return better error
messages:
"Failed to register slave: too long 'report-host'"
"Failed to register slave: too long 'report-user'"
"Failed to register slave; too long 'report-password'"

No test case for this fix.


sql/repl_failsafe.cc:
  Report descriptive error when master fails to register slave.