Fix a few $CROWBAR_TESTING issues
Fix a few $CROWBAR_TESTING issues

- barclamp-templates and autoyast profile template might not be present in
  /opt/dell/chef/ when installing from source
- Skip checks for NCC repos when $CROWBAR_TESTING is set
- Check if repos already exist before adding them
- Updated documentation

aspiers/crowbar,SUSE-Cloud/crowbar,rsalevsky/crowbar,dirkmueller/crowbar,aplanas/crowbar,MaximilianMeister/crowbar,mmnelemane/crowbar,vwallfahrer/crowbar,vwallfahrer/crowbar,rhafer/crowbar,SUSE-Cloud/crowbar,aplanas/crowbar,rhafer/crowbar,nkrinner/crowbar,rhafer/crowbar,dirkmueller/crowbar,crowbar/crowbar,nkrinner/crowbar,mmnelemane/crowbar,toabctl/crowbar,rsalevsky/crowbar,tserong/crowbar,toabctl/crowbar,crowbar/crowbar,tserong/crowbar,aspiers/crowbar,MaximilianMeister/crowbar