Add support for parameters section of the workflow.xml

[potiuk]

We should add support for additional validation/default parameters passing via parameters section of the workflow.xml . It is related to #137 and #39 and #134 but different.

The Section
Another convenient feature for parameterization is the section at the top of the workflow. This optional section allows users to declare the EL variables in the workflow XML. This lets Oozie validate the XML and the parameters before submission to the server rather than after. This is similar to a compile time check versus a runtime check in programming languages. Users can declare just a or also specify a . If there is just a name, Oozie will check for the value defined either in the job.properties file or through -D . It will throw an error if the variable is not defined. If the section also includes a element, that value will be used as the default value if the variable is not defined elsewhere. It is similar to the config-default.xml and can be used for handling defaults, though the section is confined to only that workflow file.
NOTE
Oozie’s validation of the section ignores the entries in the config-default.xml file. So use the config-default.xml file approach or the section for providing the defaults, but don’t try to mix both for a given workflow.