Remove/move down WORKDIR lines in Dockerfiles

They seem to stop Docker using its build cache.
Removing the line entirely stops weaveproxy from working, as it
assumes it can exec `./weave` from the current directory.

prog/weaveexec/Dockerfile.template

@@ -12,7 +12,6 @@ LABEL works.weave.role=system \
       org.label-schema.vcs-url="https://github.com/weaveworks/weave" \
       org.label-schema.vendor="Weaveworks"
 
-WORKDIR /home/weave
 ENTRYPOINT ["/home/weave/sigproxy", "/home/weave/weave"]
 
 RUN apk add --update \
@@ -32,3 +31,4 @@ ADD ./weavewait /w/w
 ADD ./weavewait_noop /w-noop/w
 ADD ./weavewait_nomcast /w-nomcast/w
 ADD ./docker /usr/bin/
+WORKDIR /home/weave

prog/weaver/Dockerfile.template

@@ -1,5 +1,4 @@
 FROM DOCKERHUB_USER/weaveexecARCH_EXT
-WORKDIR /home/weave
 ADD ./weaver /home/weave/
 ADD weavedata.db /weavedb/
 COPY ca-certificates.crt /etc/ssl/certs/