String-related fixes for Python 3

- Check if a variable is a strings using isinstance and six.
  At least one of the two checks before the fix triggers
  an exception visible in the logs when using internal
  job binaries ("Job binary internal data must be a string of
  length greater than zero").
- Encode a string that is passed to md5, as the error suggests
  ("Unicode-objects must be encoded before hashing")

Change-Id: Icb5d75bdbfb83070c579b9b99a395f344c3120ce

sahara/service/coordinator.py

@@ -100,7 +100,8 @@ class HashRing(Coordinator):
 
     @staticmethod
     def _hash(key):
-        return int(hashlib.md5(str(key)).hexdigest(), 16)  # nosec
+        return int(
+            hashlib.md5(str(key).encode('utf-8')).hexdigest(), 16)  # nosec
 
     def _build_ring(self):
         ring = {}

sahara/service/validations/edp/job_binary_internal.py

@@ -14,6 +14,7 @@
 # limitations under the License.
 
 from oslo_config import cfg
+import six
 
 import sahara.exceptions as e
 from sahara.i18n import _
@@ -31,7 +32,7 @@ def check_job_binary_internal(data, **kwargs):
     if not is_internal_db_enabled():
         raise e.BadJobBinaryInternalException(
             _("Sahara internal db is disabled for storing job binaries."))
-    if not (type(data) is str and len(data) > 0):
+    if not (isinstance(data, six.string_types) and len(data) > 0):
         raise e.BadJobBinaryInternalException()
     if "name" in kwargs:
         name = kwargs["name"]

sahara/utils/api.py

@@ -18,6 +18,7 @@ import traceback
 import flask
 from oslo_log import log as logging
 from oslo_middleware import request_id as oslo_req_id
+import six
 from werkzeug import datastructures
 
 from sahara import context
@@ -53,7 +54,7 @@ class Rest(flask.Blueprint):
         return self._mroute('PATCH', rule, status_code)
 
     def _mroute(self, methods, rule, status_code=None, **kw):
-        if type(methods) is str:
+        if isinstance(methods, six.string_types):
             methods = [methods]
         return self.route(rule, methods=methods, status_code=status_code, **kw)