Adjust Python 2.6 OSerror-on-EPIPE workaround

Adjust the code to raise exceptions.CertificateConfigError
when the certificates are still missing even in the Python
2.6 subprocess bug-workaround case.

Change-Id: I9fdfa830e6f9bc9e8eab496da2597e4118577ec5
Closes-Bug: #1324921
Merge "Adjust Python 2.6 OSerror-on-EPIPE workaround"