go-susi: up build dependency to golang-go >= 1.4
When compiled with go < 1.4 gosa_query_packages_list takes ages (longer than
GOsa's 15s timeout) when the database contains full trusty and jessie repository.
Compiled with go 1.4 the query typically takes less than 1s. Probably the improved GC.
For LHM internal use a go-susi compiled with an older Go is probably okay because
LHM repos have only a small subset of packages. But for the rest of the world a
go-susi compiled with Go < 1.4 is broken.