Modify instances of the use of the word idempotence to be correct. (#18704)

Idempotence has a very specific meaning and it is generally not used correctly
in the manual. My attention was first drawn to this problem by the incorrect
definition in the glossary, but on further reading of the docs I found that
the problem occurred in a number of places.

Signed-off-by: mulhern <amulhern@redhat.com>

docsite/rst/dev_guide/developing_modules.rst

@@ -149,12 +149,11 @@ a lot shorter than this::
             if key == "time":
 
                 # now we'll affect the change.  Many modules
-                # will strive to be 'idempotent', meaning they
-                # will only make changes when the desired state
-                # expressed to the module does not match
-                # the current state.  Look at 'service'
-                # or 'yum' in the main git tree for an example
-                # of how that might look.
+                # will strive to be idempotent, generally
+                # by not performing any actions if the current
+                # state is the same as the desired state.
+                # See 'service' or 'yum' in the main git tree
+                # for an illustrative example.
 
                 rc = os.system("date -s \"%s\"" % value)