[collectd] GenericJMX enhancement

[Jason Stelzer]

We are using the GenericJMX plugin to monitor Tomcat.

This produces directory names like: GenericJMX-"http-apr-7084".

I have a visualization frontend that essentially just walks trees of
rrd files and generates graphs from them. I could translate names
there, but I would rather see the filesystem have 'clean' names.

It might be nice to add a toggle so that you can normalize the names.
Is there a preferred approach to this? Should the collector plugin be
responsible for maintaining a mapping to 'actual' and 'cleaned up'
names? There are other metrics that contain whitespace, brackets,
quotes and other noise.

To this end, I modified GenericJMXConfMBean.java and added 2
configuration properties:

MaskChars is a regex of characters to mask.
ReplacementString is a string to replace the masked characters with.

A sample configuration could look like this:

  <Plugin "GenericJMX">
    # Memory usage by memory pool.
    <MBean "appname_tomcat/memory_pool">
      ObjectName "java.lang:type=MemoryPool,*"
      InstancePrefix "appname_tomcat-memory_pool-"
      InstanceFrom "name"
      MaskChars "[ ,\\%\\[\\]\"]"
      ReplacementString ""
      <Value>
        Type "memory"
        #InstancePrefix ""
        #InstanceFrom ""
        Table true
        Attribute "Usage"
      </Value>
    </MBean>
</Plugin>


What this essentially means is the following:

* When you replace substrings, it's expected you do so in a way that
is distinct and stable.
* The stats are sent to the collectd system such that the names are 'clean'.
* If you do not specify these directives, the system behaves as it did before.

Would anyone else find this feature convenient? Would you like me to
submit a patch?
-- 
J.