Use sha1 instead sha256 for our updateinfo.xml checksum on el5 (#1080373)

Yum on Python2.4 supports the sha256 checksum type only if python-hashlib is
available, but there is not a hard requirement on it.
Merge pull request #43 from fedora-infra/feature/sha1-on-el5

Use sha1 instead sha256 for our updateinfo.xml checksum on el5