containers/docker: Fix dockerfiles for new branch layout; add dockerfile in root

Dockerfile

+FROM alpine:3.3
+
+ADD . /go-ethereum
+RUN \
+  apk add --update go make gcc musl-dev             && \
+  (cd go-ethereum && make geth)                     && \
+  cp go-ethereum/build/bin/geth /geth               && \
+  apk del go make gcc musl-dev                      && \
+  rm -rf /go-ethereum && rm -rf /var/cache/apk/*
+
+EXPOSE 8545
+EXPOSE 30303
+
+ENTRYPOINT ["/geth"]

containers/docker/develop-alpine/Dockerfile

@@ -2,7 +2,7 @@ FROM alpine:3.4
 
 RUN \
   apk add --update go git make gcc musl-dev && \
-  git clone --depth 1 --branch develop https://github.com/ethereum/go-ethereum && \
+  git clone --depth 1 https://github.com/ethereum/go-ethereum && \
   (cd go-ethereum && make geth) && \
   cp go-ethereum/build/bin/geth /geth && \
   apk del go git make gcc musl-dev && \

containers/docker/master-alpine/Dockerfile

@@ -2,7 +2,7 @@ FROM alpine:3.4
 
 RUN \
   apk add --update go git make gcc musl-dev && \
-  git clone --depth 1 https://github.com/ethereum/go-ethereum && \
+  git clone --depth 1 --branch release/1.5 https://github.com/ethereum/go-ethereum && \
   (cd go-ethereum && make geth) && \
   cp go-ethereum/build/bin/geth /geth && \
   apk del go git make gcc musl-dev && \