Added proto.Message to url.Values Function for GET-Requests

[Codehardt]

Sending GET Requests with a proto.Message was not possible. The apiclient::do(...) just added the proto.Message to the POST Body.

This solution checks if the method equals GET and converts the proto.Message to url.Values. Then it is possible to call the already implemented function apiclient::get(...)

[hillu]

apiclient..do() does not add the proto.Message to the body but a JSON-serialized form of the struct.

GET requests containing a body are valid and GRR understands them, so I see no need for this change.

[Codehardt]

GET requests containing a body are valid and GRR understands them [...]

Not working for e.g. apiclient.ApiListHuntsArgs. Sending a ListHunts GET Request with JSON-Body {"count": 10, "offset": 5} does not work, but sending the ListHunts GET Request with GET Params count=10&offset=5 works.

[hillu]

Damn.

This means that we'll have to fix the code-generator for the GET and GET-simple variants.