Add isDraft property to PatchSet attribute

This property is boolean. So this patch also adds getBoolean() to
GerritEventFactory.
Update test
Add the latest version to maven plugins

Perhaps they had been declared by Jenkins project so far.
This patch prevents warning.
Property for gerrit port

By property "gerrit.ssh.port", the port for sshdservermock can be moved to
another port in StreamWatchdogTest.
Merge pull request #2 from rinrinne/draft-flag

Add isDraft property to PatchSet attribute.
Merge pull request #3 from rinrinne/dependency-version

Add the latest version to maven plugins
Merge pull request #4 from rinrinne/gerrit-port

Property for gerrit port