Add commentary about PKI admin password

Add a note in cainstance.configure_instance that "admin_password" is
the password to be used for the PKI admin account, NOT the IPA admin
password.  In fact, it is set to the Directory Manager password.

This comment would have saved me some time during recent
investigation of a replica installation issue.

Reviewed-By: Christian Heimes <cheimes@redhat.com>

ipaserver/install/cainstance.py

@@ -345,7 +345,14 @@ class CAInstance(DogtagInstance):
         self.dm_password = dm_password
         self.admin_user = "admin"
         self.admin_groups = ADMIN_GROUPS
+
+        # NOTE: "admin_password" refers to the password for PKI
+        # "admin" account.  This is not necessarily the same as
+        # the IPA admin password.  Indeed, ca.configure_instance
+        # gets called with admin_password=dm_password.
+        #
         self.admin_password = admin_password
+
         self.pkcs12_info = pkcs12_info
         if self.pkcs12_info is not None:
             self.clone = True