MASTER_POS_WAIT return values are different than expected when the server is not a slave. 
It returns -1 instead of NULL.

Fixed with correcting  st_relay_log_info::wait_for_pos() to return the proper
value in the case of rli info is not inited.


mysql-test/r/rpl_master_pos_wait.result:
  results changed
mysql-test/t/rpl_master_pos_wait.test:
  the new test to check that select master_pos_wait() to a server does 
  not have master info returns NULL as specified.
sql/slave.cc:
  changing the return value to correspond the specification.