Do not assume order of dictionary elements in init_l3

Do not assume order of dictionary elements in init_l3

This fixes the test_interface unit tests[1] that breaks with a
randomized PYTHONHASHSEED (see the bug report).

The test assumed that the init_l3 method from
neutron.agent.linux.interface had dictionary elements in a particular
order. Found with PYTHONHASHSEED=2.

The fix refactors the test case to handle unsorted dictionaries in
init_l3.

[1] neutron.tests.unit.agent.linux.test_interface.TestABCDriver

Partial-bug: #1348818

Note: There are several other unrelated unit tests that also break with
a randomized PYTHONHASHSEED, but they are not addressed here. They will
be addressed in separate patches.

Change-Id: I1948593b4d7a0069ef060512942b548c74a6b369