Split some DRBD functionality based on versions
Split some DRBD functionality based on versions

This is a small split of some functionality from the DRBDev class into a
base drbd class that holds just a few things, in order to make migration
to drbd 8.x easier.

Reviewed-by: imsnah


mbakke/ganeti,bitemyapp/ganeti,yiannist/ganeti,dimara/ganeti,andir/ganeti,grnet/snf-ganeti,leshchevds/ganeti,apyrgio/snf-ganeti,mbakke/ganeti,apyrgio/ganeti,leshchevds/ganeti,bitemyapp/ganeti,ganeti/ganeti,dimara/ganeti,mbakke/ganeti,ganeti-github-testing/ganeti-test-1,apyrgio/ganeti,andir/ganeti,yiannist/ganeti,leshchevds/ganeti,apyrgio/snf-ganeti,andir/ganeti,onponomarev/ganeti,yiannist/ganeti,ganeti/ganeti,ganeti/ganeti,grnet/snf-ganeti,ganeti-github-testing/ganeti-test-1,onponomarev/ganeti