[devel] Find certificates for XML RPC from CVMFS

Currently the software configuration database uses a certificate which is issued by the CERN Grid CA and therefore not generally trusted. As we already use CVMFS as a fallback I propose always getting the CAs from CVMFS when querying it. Thoughts?

cc @clemenci @bcouturi

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*Configuration CHANGE: Get CA certificates from CVMFS when querying the software configuration database

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