Changed kernel_id generation method name and calling scenario

Per review comments, the name of the method to generate a kernel_id
was changed to `new_kernel_id()`.  In addition, the method is now
only called if `kernel_id` is not represented in the keyword arguments
(`**kwargs`).

Author: kevin-bates

jupyter_client/multikernelmanager.py

@@ -86,11 +86,11 @@ def start_kernel(self, kernel_name=None, **kwargs):
         """Start a new kernel.
 
         The caller can pick a kernel_id by passing one in as a keyword arg,
-        otherwise one will be picked using a uuid.
+        otherwise one will be generated using new_kernel_id().
 
         The kernel ID for the newly started kernel is returned.
         """
-        kernel_id = self.determine_kernel_id(**kwargs)
+        kernel_id = kwargs.pop('kernel_id', self.new_kernel_id(**kwargs))
         if kernel_id in self:
             raise DuplicateKernelError('Kernel already exists: %s' % kernel_id)
 
@@ -316,12 +316,11 @@ def connect_hb(self, kernel_id, identity=None):
         stream : zmq Socket or ZMQStream
         """
 
-    def determine_kernel_id(self, **kwargs):
+    def new_kernel_id(self, **kwargs):
         """
-        Returns the kernel_id to use for this request.  If kernel_id is already in the arguments list,
-        that value will be used.  Otherwise, a newly generated uuid is used.  Subclasses may override
+        Returns the id to associate with the kernel for this request. Subclasses may override
         this method to substitute other sources of kernel ids.
         :param kwargs:
         :return: string-ized version 4 uuid
         """
-        return kwargs.pop('kernel_id', unicode_type(uuid.uuid4()))
+        return unicode_type(uuid.uuid4())