htcondorcern: better management of CERN certificates

[tiborsimko]

r-j-controller source code contains CERN certificates which are necessary for HTCondor integration. It was necessary recently to update them in #260. Instead of maintaining certificates in our own source code, explore option of installing an upstream package.

For example, on LXPLUS there is CERN-CA-certs-20200530-1.el7.cern.noarch which is probably not directly compatible with our Debian/Ubuntu based image, but If we install it via alien and run update certificate commands appropriately, hopefully we wouldn't have to maintain certificate blobs ourselves.

Hence action: when time permits, check installing CERN certificates either from RPM or via direct download, and remove blobs we are hosting ourselves.

(stemmed from #260)