Better EMR coverage and boto3 request/response handling

This revision includes:

- A handler for requests for which content-type is JSON (from boto3).

- A decorator (generate_boto3_response) to convert XML responses to
  JSON (for boto3). This way, existing response templates for boto can
  be shared for generating boto3 response.

- Utility class/functions to use botocore's service specification data
  (accessible under botocore.data) for type casting, from query
  parameters to Python objects and XML to JSON.

- Updates to response handlers/models to cover more EMR end points and
  mockable parameters

moto/emr/utils.py

@@ -1,19 +1,25 @@
 from __future__ import unicode_literals
 import random
 import string
+
 import six
 
 
-def random_job_id(size=13):
+def random_id(size=13):
     chars = list(range(10)) + list(string.ascii_uppercase)
-    job_tag = ''.join(six.text_type(random.choice(chars)) for x in range(size))
-    return 'j-{0}'.format(job_tag)
+    return ''.join(six.text_type(random.choice(chars)) for x in range(size))
+
+
+def random_cluster_id(size=13):
+    return 'j-{0}'.format(random_id())
+
+
+def random_step_id(size=13):
+    return 's-{0}'.format(random_id())
 
 
 def random_instance_group_id(size=13):
-    chars = list(range(10)) + list(string.ascii_uppercase)
-    job_tag = ''.join(six.text_type(random.choice(chars)) for x in range(size))
-    return 'i-{0}'.format(job_tag)
+    return 'i-{0}'.format(random_id())
 
 
 def tags_from_query_string(querystring_dict):
@@ -30,3 +36,18 @@ def tags_from_query_string(querystring_dict):
             else:
                 response_values[tag_key] = None
     return response_values
+
+
+def steps_from_query_string(querystring_dict):
+    steps = []
+    for step in querystring_dict:
+        step['jar'] = step.pop('hadoop_jar_step._jar')
+        step['properties'] = dict((o['Key'], o['Value']) for o in step.get('properties', []))
+        step['args'] = []
+        idx = 1
+        keyfmt = 'hadoop_jar_step._args.member.{0}'
+        while keyfmt.format(idx) in step:
+            step['args'].append(step.pop(keyfmt.format(idx)))
+            idx += 1
+        steps.append(step)
+    return steps