PDI-7243/PDI-11183 - JSON Output Step throws NullPointerException when previewing no rows

PDI-11183 - fixed
PDI-7243 - patch applyed, junit tests
PDI-11183 - junit tests added
PDI-8395 - JSON Output step only outputs last line of transformation if
append is not checked.

junit tests added
PDI-8395 - JSON Output step only outputs last line of transformation if
append is not checked.

fix added
PDI-7243 - JSON Output Step throws NullPointerException when previewing
no rows

Fix patch to be compatible with old behaviour
Checkstyle for junit test, System.out removed
Remove dependancy on reporting packages

Remove unnecessary dependancy, null aware String comparsion can be done
easily.
modified:   engine/src/org/pentaho/di/job/entries/getpop/MailConnectionMeta.java
Merge pull request #200 from prakapenka/PDI-7243

PDI-7243, PDI-11183, PDI-8395  - cummulative fix for JsonOutput step.