build: added Dockerfile + binaries generator bash script

Updates #61

.gitignore

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+bin/
+
+# Miscellaneous files
+*.sw[op]
+*.DS_Store

Dockerfile

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+FROM debian:jessie
+
+COPY ./bin/ocagent_linux ocagent
+
+# Expose the OpenCensus interceptor port
+EXPOSE 55678/tcp
+
+CMD ["ocagent"]

build_binaries.sh

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+#!/bin/bash
+
+# Copyright 2018, OpenCensus Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# This file is useful to help build binaries or the Docker image
+# Usage:
+#   It provides a couple of commands like:
+# a) Building binaries by passing in the GOOS value e.g.
+#    darwin
+#    linux
+#    windows
+#
+# b) Build all the binaries by passing in: binaries
+#
+# c) Building the Docker image:
+#    By passing in argument "docker" and optionally the version to be tagged otherwise it'll be "v0.0.1"
+
+
+if [[ $# -lt 1 ]]
+then
+    echo -e "Usage: $0 <cmd>\nwhere <cmd> is any of 'docker' 'binaries' or GOOS such as:\ndarwin\nlinux\nwindows"
+    exit
+fi
+
+function build() {
+    GOOS="$1"
+    CMD="GOOS=$GOOS go build -o bin/ocagent_$GOOS ./cmd/ocagent"
+    echo $CMD
+    eval $CMD
+}
+
+function buildAll() {
+    build darwin
+    build linux
+    build windows
+}
+
+function dockerBuild() {
+    build linux
+    VERSION="$1"
+    if [[ "$VERSION" == "" ]]
+    then
+        VERSION="v0.0.1"
+    fi
+
+    CMD="docker build -t ocagent:$VERSION ."
+    echo $CMD
+    eval $CMD
+}
+
+case $1 in
+"docker")
+    dockerBuild $2;;
+"binaries")
+    buildAll;;
+*)
+    build "$1"
+esac