Remove internal helper _default_security_group

_default_security_group is used only once, so this is
to remove it and to put the code logic directly in
_create_security_group_rule.

Besides, change to using filter parameter in list_security_groups
to get tenant's default security_groups, which should be equivalent
to filter result from list_security_groups(), and will make code
a bit clearer.

Change-Id: I94fdaa36624e290a03fa68563210f4521e581231
1 file changed