distro/deb: generate knot-dbg package explicitly
This is a workaround for OpenBuildService, which doesn't properly auto-generate *-dbgsym packages for Ubuntu.
knot-dbg package now contains all debug symbols, for daemon, tools and libraries - instead of having multiple *-dbgsym packages, separate for each package.
Please backport to 2.8 as well.
Edited by Tomas Krizek