veyron/services/mgmt/build: respecting the GOROOT environment variable setting in order to make the build server test pass with Go 1.4
veyron/services/mgmt/build: respecting the GOROOT environment variable
setting in order to make the build server test pass with Go 1.4

Change-Id: If6b8430b1cf491b4fc4d2e3d9ef1cfdbb3ce4877

vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref