scripts: fix gceworker for go 1.7.1
scripts: fix gceworker for go 1.7.1

The script was trying to install `parallelbuilds-go1.7.1.patch`. Fixing to
extract only the first two numbers from the version.

veteranlu/cockroach,glycerine/cockroach,maxlang/cockroach,maxlang/cockroach,petermattis/cockroach,cockroachdb/cockroach,paperstreet/cockroach,cockroachdb/cockroach,vaibhavarora/cockroach,paperstreet/cockroach,vaibhavarora/cockroach,maxlang/cockroach,paperstreet/cockroach,cockroachdb/cockroach,cockroachdb/cockroach,veteranlu/cockroach,vaibhavarora/cockroach,glycerine/cockroach,veteranlu/cockroach,glycerine/cockroach,glycerine/cockroach,maxlang/cockroach,petermattis/cockroach,paperstreet/cockroach,maxlang/cockroach,cockroachdb/cockroach,petermattis/cockroach,petermattis/cockroach,petermattis/cockroach,paperstreet/cockroach,glycerine/cockroach,glycerine/cockroach,vaibhavarora/cockroach,vaibhavarora/cockroach,veteranlu/cockroach,veteranlu/cockroach,vaibhavarora/cockroach,paperstreet/cockroach,vaibhavarora/cockroach,petermattis/cockroach,cockroachdb/cockroach,cockroachdb/cockroach,petermattis/cockroach,veteranlu/cockroach,veteranlu/cockroach,maxlang/cockroach,glycerine/cockroach,glycerine/cockroach,maxlang/cockroach,vaibhavarora/cockroach,maxlang/cockroach,petermattis/cockroach,cockroachdb/cockroach,paperstreet/cockroach,veteranlu/cockroach,paperstreet/cockroach