There is quite a bit going on in this commit. At a high-level this
improves the config subcommand so that it can support more value type
and not just strings. To do this we need to know the schema for each
subsection. The config subcommand queries all of the subcommands for
this information. Here are all of the changes includes in this commit:
* Fix the makefile so that the test, doc and packages target depend on
env.
* Add support for append, prepend, unset a list element and validate in
the config subcommand.
* Extend the marathon, package and subcommand subcommands so that they
return the schema for their section of the config file.
* Adds config schema file the python package.
* The module jsonschema returns poorly formatted validation errors. This
commit includes regular expression to clean up those messages.
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