Allow setting tags from the init default file

This change let us add some extra tags to be added by
the agent from the init script's default file. This is
useful for setting thing like data centre location.

It also includes some changes to the JMX based hadoop 
collectors to use jps to determine the PID, rather than letting
the jmx tool scan for it. This resulted in more reliable 
connections from us.

It also lets the hbase collector ignore some mbeans that produce
bad values, as per the datanode collector