Add a hacking rule for non-existent assertions

Add a hacking rule for non-existent mock assertion methods and
attributes.

[N364] Non existent mock assertion method or attribute (<name>) is used.
       Check a typo or whether the assertion method should begin with
       'assert_'.

Change-Id: Ic6860e373120086a1a2ae9953f09a7bbaa032a7b

HACKING.rst

@@ -74,6 +74,7 @@ Nova Specific Commandments
   not "from nova.privsep import path". This ensures callers know that the method they're
   calling is using priviledge escalation.
 - [N363] Disallow ``(not_a_tuple)`` because you meant ``(a_tuple_of_one,)``.
+- [N364] Check non-existent mock assertion methods and attributes.
 
 Creating Unit Tests
 -------------------