Reduce messages in console when waiting for start server to complete

[cherylking]

The following message appears repeatedly while waiting for the server to start. Optimize the logic to only print the message once.

CWWKM2013I: The file {0} being validated does not exist.

This is logged in AbstractTask.findStringsInFileCommon() method, which is called by findStringInFile(), which is called by waitForStringInLog() in a loop based on the serverStartTimeout value.