Dockerfile entrypoint ensures dependencies and builds plugins

This patch extends Dockerfile entrypoint with plugin build action.
Conventional location for plugin folder under container environment is
/go/src/flowd/plugins. The entrypoint iteratively builds all plugins
inside this folder.

Docker build command example:
    docker build -t awesome-flow/flow:latest .

Docker run command example:
    docker run -it -p 8080:8080 -p 7071:7071 --rm \
        -v "${GOPATH}/src/github.com/awesome-flow/flow/examples:/etc/flowd/" \
	awesome-flow/flow:latest \
	-config.path=/etc/flowd/http2stdout-config.yml

Signed-off-by: Oleg Sidorov <[email protected]>

Author: Oleg Sidorov

Diff for: .dockerignore

@@ -2,3 +2,4 @@
 vendor/*/.git
 vendor/*/*/.git
 vendor/*/*/*/.git
+builds/*

Diff for: Dockerfile

@@ -1,6 +1,9 @@
 FROM golang:1.12-alpine
 RUN apk add build-base
+RUN apk add git
 WORKDIR /go/src/github.com/awesome-flow/flow/
 ADD . .
+RUN go get -u github.com/golang/dep/cmd/dep
+RUN dep ensure
 RUN make build
-ENTRYPOINT ["./builds/flowd"]
+ENTRYPOINT ["sh", "./docker/flowd-runner.sh"]

Diff for: docker/flowd-runner.sh

@@ -0,0 +1,37 @@
+set -e
+
+FLOWD=./builds/flowd
+PLUGIN_PATH="/go/src/flowd/plugins/"
+
+build_plugin () {
+	plugin="${1}"
+	echo "Building plugin ${plugin}"
+	cd "${plugin}"
+	if test -f go.mod
+	then
+		go mod verify
+	fi
+	if test -d Gopkg.toml
+	then
+		dep ensure
+	fi
+	go build -buildmode=plugin
+	cd ..
+}
+
+if test -d ${PLUGIN_PATH}
+then
+	oldpath=$(pwd)
+	cd "${PLUGIN_PATH}"
+	for p in $(ls -l .); do
+		if test -d $p
+		then
+			build_plugin "${p}"
+		fi
+	done
+	cd "${oldpath}"
+fi
+
+echo "Launching flowd"
+dep ensure
+${FLOWD} -plugin.path="${PLUGIN_PATH}" $@