[Dynamo.HTTP.Case] Allow to pass a body to process

Signed-off-by: chatgris <jboyer@af83.com>
Add a failing test on conn.req_body

Signed-off-by: chatgris <jboyer@af83.com>
Hopefully, this should fix fetch of body in TestCase

Signed-off-by: chatgris <jboyer@af83.com>