Membership ephemeral entry and initial leader election

Also:
- env.sh to load what's needed for dev
- refactored main
- async consul client instead of blocking
diff --git a/Dockerfile b/Dockerfile
index 1a9ecc4..03537b8 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -27,9 +27,9 @@
 COPY requirements.txt /tmp/requirements.txt
 
 # Install app dependencies
-RUN apk add build-base gcc abuild binutils python-dev libffi-dev openssl-dev && \
+RUN apk add build-base gcc abuild binutils python-dev libffi-dev openssl-dev git && \
     pip install -r /tmp/requirements.txt && \
-    apk del --purge build-base gcc abuild binutils python-dev libffi-dev openssl-dev
+    apk del --purge build-base gcc abuild binutils python-dev libffi-dev openssl-dev git
 
 # Bundle app source
 COPY voltha /voltha