DIRACGrid/DIRACOS: v1r17

This release contains the following PRs CHANGE: (#156) Fix pip version to 20.2.4 (20.3 does not work) CHANGE: (#156) Update mock config files to use Centos Vault and EPEL from Fedora Archive CHANGE: (#156) Use dedicated container diracgrid/centos6 for building that has Centos Vault and EPEL from Fedora Archive enabled CHANGE: (#161) davix 0.7.5 -> davix 0.7.6 devel CHANGE: (#161) gfal2.17.1 -> gfal2.19.0 (final RC) FIX: (#159) Fix M2Crypto to 0.36 due to swig problem in future versions FIX: (#160) adjust test to new DIRAC folder layout FIX: (#162) Force pip version in CI to be