Check for docbook2{man,pdf,html}
Check for docbook2{man,pdf,html}

docbook2{man,pdf,html} are mandatory. "configure" aborts if one
of them isn't found.

Reviewed-by: iustinp


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