Remove duplicate setup code from test_tempurl.py
Remove duplicate setup code from test_tempurl.py

TestTempURLPrefix.setUp() almost duplicates the superclass
setUp method, except it set "expires" as an instance variable.
The duplicated setUp code can be removed by simply having the
super class setUp set the "expires" instance variable.

Change-Id: Icf7604460e475523e156daa8c578765336820c8e

openstack/swift,clayg/swift,notmyname/swift,tipabu/swift,nadeemsyed/swift,swiftstack/swift,matthewoliver/swift,notmyname/swift,matthewoliver/swift,smerritt/swift,matthewoliver/swift,matthewoliver/swift,tipabu/swift,psachin/swift,psachin/swift,notmyname/swift,nadeemsyed/swift,nadeemsyed/swift,swiftstack/swift,redbo/swift,smerritt/swift,swiftstack/swift,psachin/swift,clayg/swift,tipabu/swift,psachin/swift,openstack/swift,openstack/swift,clayg/swift,clayg/swift,tipabu/swift,notmyname/swift,smerritt/swift,openstack/swift,nadeemsyed/swift,smerritt/swift,redbo/swift