should not use mutable default arguments

[javeme]

We should not use mutable default arguments in function definitions due to the "Common Gotchas"[1].

So, we must remove the default arguments "[]" when the function is defined, such as this function:
https://github.com/openstack/horizon/blob/master/openstack_dashboard/utils/metering.py#L178

[1]: http://docs.python-guide.org/en/latest/writing/gotchas/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/256931
Committed: https://git.openstack.org/cgit/openstack/horizon/commit/?id=db8e206bee856fe838b381e5dc8eb47706f50b5b
Submitter: Jenkins
Branch: master

commit db8e206bee856fe838b381e5dc8eb47706f50b5b
Author: Javeme <email address hidden>
Date: Sat Dec 12 18:28:58 2015 +0800

    remove the default arguments "[]"

    remove the default arguments "[]" when the function is defined.
    ref: http://docs.python-guide.org/en/latest/writing/gotchas/

    Closes-Bug: #1525903
    Change-Id: I241f22fe10e535bb50f7ce27fac09d6448fd2bb2

[Doug Hellmann (doug-hellmann)]

This issue was fixed in the openstack/horizon 9.0.0.0b2 development milestone.