Use JSONSchema as our only JSON validation tool

As of now in Watcher both jsonschema and voluptuous are used to validate JSON payloads. However, the problem with voluptuous is that its structure is not standardized compare to jsonschema which means that we cannot easily expose the validation schema through our API.

As of now, voluptuous is used to:

- validate the input parameters of a Watcher action when it gets to the Applier.
- validate the efficacy indicators

Here below is an explanation of the problem from a discussion
(17:15:30) vfrancoise: https://blueprints.launchpad.net/watcher/+spec/jsonschema-validation this one is similar
(17:19:36) Yumeng__: So we need to change existed voluptuous to jsonschema
(17:19:44) vfrancoise: yes
(17:20:10) vfrancoise: because voluptuous is not really serializable
(17:20:32) vfrancoise: let me show you what bothers me in the code that has to be fixed
(17:20:51) Yumeng__: Ok, greate
(17:21:46) vfrancoise: a good definition of done is that we should be able to remove the voluptuous dependency once you've finished this BP
(17:21:59) vfrancoise: but there is one tricky part
(17:23:39) vfrancoise: give me a sec I can't remember where it is :p
(17:24:35) Yumeng__: No problem. Take your time
(17:27:35) vfrancoise: ok so that here https://github.com/openstack/watcher/blob/master/watcher/decision_engine/goal/efficacy/base.py#L65-L74
(17:29:05) vfrancoise: basically, we are collecting the voluptuous schemas from all the efficacy indicators to form one big schema that is used to validate all the inputs
(17:32:56) Yumeng__: So now we need to use jsonschema to replace the big volupous scheme?
(17:36:17) vfrancoise: yes, you need to find a way to combine many jsonschema into a big one
(17:38:49) Yumeng__: But why we need to combine schemas into a one big scheme to validate all the inputs?
(17:39:09) vfrancoise: because we want to expose it via the API later on
(17:39:41) vfrancoise: efficacy specifications are part of the /goal API
(17:40:32) vfrancoise: look at https://github.com/openstack/watcher/blob/master/watcher/api/controllers/v1/goal.py#L108-L113
(17:41:35) vfrancoise: the serialization of the schema only works because it's a valid python string so we can interprete it but that's really not a good practice
(17:41:40) Yumeng__: So the big schema is like a interface, and for a specific efficacy indicator we validate it using a specific schema in the big schema?
(17:41:54) vfrancoise: also the idea is to simplify the code so we only use jsonschema for validation
(17:43:00) vfrancoise: yes you got it
(17:43:33) vfrancoise: we do this serialization so we don't introduce a strong coupling between the watcher API and the watcher Applier
(17:43:43) vfrancoise: so we use the schema as a validation contract