Update `gotools` and `amptools` images to use fixed versions

[ndegory]

I think it's already the case (since #1668):

$ grep appcelerator/amptools cmd/ampmake/main.go
    toolsImage      = "appcelerator/amptools:1.7"

Do you think of other places where we use the image without tag?

[neha-viswanathan]

It's for these packages in the image:

• github.com/golang/protobuf
• google.golang.org/grpc/grpc-go
• github.com/grpc-ecosystem/grpc-gateway
• github.com/golang/glog
• google.golang.org/genproto
• github.com/alecthomas/gometalinter

[ndegory]

ok, got it