fix time-sensitive tests in expiring objects

[John Dickinson]

I noticed that a couple of tests I recently made were
time-sensitive. This can be shown with the following quick
script:

from sys import exit
from unittest import TestSuite, TextTestRunner

from test.unit.obj.test_server import TestObjectController

s = TestSuite()
s.addTest(TestObjectController('test_GET_but_expired'))
s.addTest(TestObjectController('test_HEAD_but_expired'))
for x in xrange(200):
    if TextTestRunner().run(s).failures:
        exit('!!!!!!!!!!!!!!! TEST FAILED !!!!!!!!!!!!!!!')
print '\o/ Test ran 200 times without failure.'