Break up the build process in 2.

This will produce an extra layer but will improve on build time because
we'll be updating Embark more frequently than the surrounding tools
(geth and IPFS.)

Also, doing this negates the need to `sudo - embark` a bunch of commands
we previously had to.

Additionally, create and use a workdir.

Dockerfile

@@ -2,7 +2,7 @@ FROM node:8.11.3-stretch
 
 MAINTAINER Andre Medeiros <andre@status.im>
 
-ENV EMBARK_VERSION=3.1.4 \
+ENV EMBARK_VERSION=3.1.5 \
     GANACHE_VERSION=6.1.4 \
     GETH_VERSION=1.8.11-dea1ce05 \
     IPFS_VERSION=0.4.15
@@ -34,9 +34,13 @@ RUN adduser --disabled-password --shell /bin/bash --gecos "" embark \
     && tar -xvzf "go-ipfs_v${IPFS_VERSION}_linux-amd64.tar.gz" \
     && cp go-ipfs/ipfs /usr/local/bin/ipfs \
     && rm -rf go-ipfs "go-ipfs_v${IPFS_VERSION}_linux-amd64.tar.gz" \
-    # Setup ~embark
-    && su - embark -c "mkdir /home/embark/.npm-packages" \
-    && su - embark -c "echo prefix=/home/embark/.npm-packages > /home/embark/.npmrc" \
+    && mkdir /dapp \
+    && chown embark:embark /dapp
+
+USER embark
+
+RUN mkdir /home/embark/.npm-packages \
+    && echo prefix=/home/embark/.npm-packages > /home/embark/.npmrc \
     && for directive in \
       "export NPM_PACKAGES=\$HOME/.npm-packages" \
       "export NODE_PATH=\$NPM_PACKAGES/lib/node_modules:\$NODE_PATH" \
@@ -45,12 +49,16 @@ RUN adduser --disabled-password --shell /bin/bash --gecos "" embark \
       echo ${directive} >> /home/embark/.profile \
       && echo ${directive} >> /home/embark/.bashrc; \
     done \
+    # Ensure we source the updated bashrc
+    && . ~/.bashrc \
     # Install embark and the simulator
-    && su - embark -c "npm install -g embark@${EMBARK_VERSION} ganache-cli@${GANACHE_VERSION}" \
+    && npm install -g "embark@${EMBARK_VERSION}" "ganache-cli@${GANACHE_VERSION}" \
+    # Initialize IPFS
+    && ipfs init \
     # Cleanup build stuff
     && echo "Done"
 
-USER embark
+WORKDIR /dapp
 
 CMD ["embark"]