Depending on test order (and possibly whether there were earlier
failures?) the new tests may trip KeyErrors when trying to get
s3_access_key values. Solution seems to be defining
setUpModule() / tearDownModule() like other functional tests.
Also fix up some Content-MD5 handling; if we're using pre-signed URLs,
we can't provide a Content-MD5.
Change-Id: Ifce72ec255b1b618b9914ce5785d04ee0ebd3b8c
Related-Change: I84494123cfc85e234098c554ecd3e77981f8a096