Fix Makefile's all target (#3085)

- Rename get_dev_tools to devtools
- tools and devtools now create a stamp after execution so
  that they are not executed twice on the same pipeline
- Add clean target to remove stamps

Dockerfile

@@ -15,7 +15,7 @@ COPY . .
 
 # Install minimum necessary dependencies, build Cosmos SDK, remove packages
 RUN apk add --no-cache $PACKAGES && \
-    make get_tools && \
+    make tools && \
     make get_vendor_deps && \
     make build && \
     make install