Add Dockerfile that resembles the Travis environment

Dockerfile

@@ -0,0 +1,55 @@
+# This Dockerfiles configures a container that is similar to the Travis CI
+# environment and can be used to run tests locally.
+#
+# build the image:
+#   docker build -t restic/test .
+#
+# run tests:
+#   docker run --rm -v $PWD:/home/travis/gopath/src/github.com/restic/restic restic/test go run run_integration_tests.go
+#
+# run interactively with:
+#   docker run --interactive --tty --rm -v $PWD:/home/travis/gopath/src/github.com/restic/restic restic/test /bin/bash
+#
+# run a tests:
+#   docker run --rm -v $PWD:/home/travis/gopath/src/github.com/restic/restic restic/test go test -v ./backend
+
+FROM ubuntu:14.04
+
+ARG GOVERSION=1.5.2
+ARG GOARCH=amd64
+
+# install dependencies
+RUN apt-get update
+RUN apt-get install -y --no-install-recommends ca-certificates wget git
+
+# download and install Go
+RUN wget -q -O /tmp/go.tar.gz https://storage.googleapis.com/golang/go${GOVERSION}.linux-${GOARCH}.tar.gz
+RUN cd /var/lib && tar xf /tmp/go.tar.gz
+RUN rm -f /tmp/go.tar.gz
+
+ENV GOROOT /var/lib/go
+ENV PATH $PATH:$GOROOT/bin
+
+# add and configure user
+ENV HOME /home/travis
+ENV GOPATH $HOME/gopath
+ENV PATH $PATH:$GOPATH/bin
+RUN useradd -m -d $HOME -s /bin/bash travis
+
+# run everything below as user travis
+USER travis
+WORKDIR $HOME
+
+# make gopath
+RUN mkdir -p $GOPATH/src/github.com/restic/restic
+
+# install tools
+RUN go get golang.org/x/tools/cmd/cover
+RUN go get github.com/mattn/goveralls
+RUN go get github.com/mitchellh/gox
+
+# set TRAVIS_BUILD_DIR for integration script
+ENV TRAVIS_BUILD_DIR $GOPATH/src/github.com/restic/restic
+ENV GOPATH $GOPATH:${TRAVIS_BUILD_DIR}/Godeps/_workspace
+
+WORKDIR $TRAVIS_BUILD_DIR