Add a maintainer-clean makefile rule
Add a maintainer-clean makefile rule

This splits the current “clean” rule into proper clean (cleaning of
build artifacts) and maintainer-clean (cleaning of distributed files).
This should make it better for Debian packaging.

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