fission/builder image, log collection improvement in builder (#397)

Create a container image with the buidler, so we can avoid copying the builder binary into the env container during the env container build. 

Gather both stdout and stderr of a build into the logs.
 

* Add Dockerfile for builder + update release scripts

* Improve logging of buildermgr and builder

* Add support for environment-scoped buildcmd

* Fix fork/exec wd when package is a file

* Update tests to also include builder image

* Add logging to builder's fork/exec

.travis.yml

@@ -12,6 +12,13 @@ cache:
     - $HOME/google-cloud-sdk/
     - $HOME/k8scli
 
+services:
+  - docker
+
+before_install:
+  - sudo apt-get update
+  - sudo apt-get -y -o Dpkg::Options::="--force-confnew" install docker-ce
+
 install:
   - go get github.com/Masterminds/glide
   - hack/travis-kube-setup.sh