upd(all): docker image build improvements

Dockerfile.api-messaging

@@ -1,5 +1,5 @@
 ## builder image
-FROM golang:1.10-alpine AS builder
+FROM crusttech/crust-builder AS builder
 
 WORKDIR /go/src/github.com/crusttech/crust
 
@@ -16,7 +16,6 @@ RUN mkdir /build; \
 ## target image
 FROM alpine:3.7
 
-ENV PATH="/crust:{$PATH}"
 WORKDIR /crust
 
 COPY --from=builder /build/* /crust/