NXCALS-1815 Adjust to ansible v2.6.0 and common-download role

#Merge request template @acc-logging-team - please have a look for approval.

This MR introduces ansible 2.6.0 with updated core structure based on the latest established conventions

An effort has been also in place here, to resolve as many deprecation warnings as possible.

Moreover, by this upgrade we overcome the issues with include_role keyword, so we open to new ansible functionality, like common tasks/roles. In this MR we adjust to common-download role, with default, integrated retry policy.

How can I get ansible 2.6 running on my environment?

Please follow the corresponding documentation, created on getting started with development page on BE-CO wikis and find out how: https://wikis.cern.ch/display/NXCALS/NXCALS+-+Getting+started+with+development#NXCALS-Gettingstartedwithdevelopment-SetupPythonenvironmentandAnsibleinstallation

Closes NXCALS-1815