Add property which desactivate build failed when source directory is not found

If you add configuration 

</configuration>
  <sourceDirFailed>false</sourceDirFailed>
  ...
</configuration>

build no failed if property source directory does not exist. Only log is print.

[INFO] -------------------------------------------------------
[INFO]  P E R F O R M A N C E    T E S T S
[INFO] -------------------------------------------------------
[INFO]  
[INFO] Property source directory '/home/user/project/src/test/jmeter' does not exist!
[INFO]  
[INFO]  
[INFO] Test Results:
[INFO]  
[INFO] Tests Run: 0, Failures: 0
[INFO]