Load Session from Zipfile

When attempting to use botocore / boto3 in AWS EMR or PySpark, it's necessary to load from a zipfile. However, botocore does not support this.

```
+ PYTHONPATH=botocore.zip:boto3.zip
+ .venv/bin/python -c 'import boto3; client=boto3.client("rds")'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/private/var/folders/4f/2ps6fjrj2kn4klgq638844bc0000gq/T/tmp.TKx8uF60/boto3.zip/boto3/__init__.py", line 91, in client
  File "/private/var/folders/4f/2ps6fjrj2kn4klgq638844bc0000gq/T/tmp.TKx8uF60/boto3.zip/boto3/session.py", line 258, in client
  File "/private/var/folders/4f/2ps6fjrj2kn4klgq638844bc0000gq/T/tmp.TKx8uF60/botocore.zip/botocore/session.py", line 827, in create_client
  File "/private/var/folders/4f/2ps6fjrj2kn4klgq638844bc0000gq/T/tmp.TKx8uF60/botocore.zip/botocore/session.py", line 700, in _get_internal_component
  File "/private/var/folders/4f/2ps6fjrj2kn4klgq638844bc0000gq/T/tmp.TKx8uF60/botocore.zip/botocore/session.py", line 924, in get_component
  File "/private/var/folders/4f/2ps6fjrj2kn4klgq638844bc0000gq/T/tmp.TKx8uF60/botocore.zip/botocore/session.py", line 163, in create_default_resolver
  File "/private/var/folders/4f/2ps6fjrj2kn4klgq638844bc0000gq/T/tmp.TKx8uF60/botocore.zip/botocore/loaders.py", line 132, in _wrapper
  File "/private/var/folders/4f/2ps6fjrj2kn4klgq638844bc0000gq/T/tmp.TKx8uF60/botocore.zip/botocore/loaders.py", line 424, in load_data
botocore.exceptions.DataNotFoundError: Unable to load data for: endpoints
```

This is a re-submission of #1969 [with permission from @gliptak](#1969 (comment)), the original author.

botocore/__init__.py

@@ -60,8 +60,6 @@ def emit(self, record):
 # individual case.
 ScalarTypes = ('string', 'integer', 'boolean', 'timestamp', 'float', 'double')
 
-BOTOCORE_ROOT = os.path.dirname(os.path.abspath(__file__))
-
 
 # Used to specify anonymous (unsigned) request signature
 class UNSIGNED(object):

botocore/loaders.py

@@ -104,7 +104,8 @@
 import logging
 import os
 
-from botocore import BOTOCORE_ROOT
+import pkg_resources
+
 from botocore.compat import OrderedDict, json
 from botocore.exceptions import DataNotFoundError, UnknownServiceError
 from botocore.utils import deep_merge
@@ -209,7 +210,7 @@ class Loader(object):
     """
     FILE_LOADER_CLASS = JSONFileLoader
     # The included models in botocore/data/ that we ship with botocore.
-    BUILTIN_DATA_PATH = os.path.join(BOTOCORE_ROOT, 'data')
+    BUILTIN_DATA_PATH = pkg_resources.resource_filename('botocore', 'data')
     # For convenience we automatically add ~/.aws/models to the data path.
     CUSTOMER_DATA_PATH = os.path.join(os.path.expanduser('~'),
                                       '.aws', 'models')

tests/functional/test_zip.py

@@ -0,0 +1,20 @@
+import shutil
+import tempfile
+import os
+import nose
+import sys
+from tests import BaseSessionTest
+
+class ZipTest(BaseSessionTest):
+    def test_load_from_zip(self):
+        fd, temp_path = tempfile.mkstemp(suffix='.zip')
+        root, ext = os.path.splitext(temp_path)
+        shutil.make_archive(root, 'zip', '../..')
+        sys.path.insert(0, temp_path)
+        super(ZipTest, self).setUp()
+        self.region = 'us-west-2'
+        self.client = self.session.create_client(
+            's3', self.region)
+        sys.path.remove(temp_path)
+        os.close(fd)
+        os.remove(temp_path)