Provide notification level to gerrit command

Now notification level feature is provided to REST API only.

This patch provides this feature to Gerrit command as parameter
named 'NOTIFICATION_LEVEL'.

Note that this parameter always 'ALL' at build started.
It's a default value if ReviewInput has no Notify attribute.
Merge pull request #177 from rinrinne/notify-for-ssh

Provide notification level to gerrit command