circleci: enable docker based hive testing

circle.yml

+machine:
+  services:
+    - docker
+
+dependencies:
+  cache_directories:
+    - "~/.ethash" # Cache the ethash DAG generated by hive for consecutive builds
+    - "~/.docker" # Cache all docker images manually to avoid lengthy rebuilds
+  override:
+    # Restore all previously cached docker images
+    - mkdir -p ~/.docker
+    - for img in `ls ~/.docker`; do docker load -i ~/.docker/$img; done
+
+    # Pull in and hive, restore cached ethash DAGs and do a dry run
+    - go get -u github.com/karalabe/hive
+    - (cd ~/.go_workspace/src/github.com/karalabe/hive && mkdir -p workspace/ethash/ ~/.ethash)
+    - (cd ~/.go_workspace/src/github.com/karalabe/hive && cp -r ~/.ethash/. workspace/ethash/)
+    - (cd ~/.go_workspace/src/github.com/karalabe/hive && hive --docker-noshell --client=NONE --test=. --sim=. --loglevel=6)
+
+    # Cache all the docker images and the ethash DAGs
+    - for img in `docker images | grep -v "^<none>" | tail -n +2 | awk '{print $1}'`; do docker save $img > ~/.docker/`echo $img | tr '/' ':'`.tar; done
+    - cp -r ~/.go_workspace/src/github.com/karalabe/hive/workspace/ethash/. ~/.ethash
+
+test:
+  override:
+    # Build Geth and move into a known folder
+    - make geth
+    - cp ./build/bin/geth $HOME/geth
+
+    # Run hive and move all generated logs into the public artifacts folder
+    - (cd ~/.go_workspace/src/github.com/karalabe/hive && hive --docker-noshell --client=go-ethereum:local --override=$HOME/geth --test=. --sim=.)
+    - cp -r ~/.go_workspace/src/github.com/karalabe/hive/workspace/logs/* $CIRCLE_ARTIFACTS