THRIFT-4448: Golang: do something with context.Context. Remove Go1.6 compatibility.
Client: go

This closes #1459
diff --git a/build/docker/README.md b/build/docker/README.md
index d7a0126..c2b203b 100644
--- a/build/docker/README.md
+++ b/build/docker/README.md
@@ -148,7 +148,7 @@
 | delphi    |               |               | Not in CI |
 | dotnet    | 2.1.4         | 2.1.4         | v2.1.4 SDK uses v2.0.5 Runtime |
 | erlang    | 18.3          | 20.0.4        |       |
-| go        | 1.6.2         | 1.8.3         |       |
+| go        | 1.7.6         | 1.9.4         | THRIFT-4516: avoid 1.10 |
 | haskell   | 7.10.3        | 8.0.2         |       |
 | haxe      | 3.2.1         | 3.4.4         | THRIFT-4352: avoid 3.4.2 |
 | java      | 1.8.0_151     | 1.8.0_151     |       |
@@ -164,5 +164,3 @@
 | rust      | 1.17.0        | 1.21.0        |       |
 | smalltalk |               |               | Not in CI |
 | swift     |               |               | Not in CI |
-
-
diff --git a/build/docker/ubuntu-artful/Dockerfile b/build/docker/ubuntu-artful/Dockerfile
index 416d75e..dacaa28 100644
--- a/build/docker/ubuntu-artful/Dockerfile
+++ b/build/docker/ubuntu-artful/Dockerfile
@@ -18,6 +18,7 @@
 # - dart: does not come with Ubuntu
 # - dotnet: does not come with Ubuntu
 # - haxe: version 3.4.2 that comes with Ubuntu cores in our CI build
+# - go: xenial comes with 1.8, we want the latest (supported)
 # - nodejs: want v8, Ubuntu comes with v6
 #
 
@@ -140,10 +141,15 @@
 `# GlibC dependencies` \
       libglib2.0-dev
 
-RUN apt-get install -y --no-install-recommends \
-`# golang (go) dependencies` \
-      golang-go \
-      golang-race-detector-runtime
+# golang
+ENV GOLANG_VERSION 1.9.4
+ENV GOLANG_DOWNLOAD_URL https://golang.org/dl/go$GOLANG_VERSION.linux-amd64.tar.gz
+ENV GOLANG_DOWNLOAD_SHA256 15b0937615809f87321a457bb1265f946f9f6e736c563d6c5e0bd2c22e44f779
+RUN curl -fsSL "$GOLANG_DOWNLOAD_URL" -o golang.tar.gz && \
+      echo "$GOLANG_DOWNLOAD_SHA256  golang.tar.gz" | sha256sum -c - && \
+            tar -C /usr/local -xzf golang.tar.gz && \
+                  ln -s /usr/local/go/bin/go /usr/local/bin && \
+                        rm golang.tar.gz
 
 RUN apt-get install -y --no-install-recommends \
 `# Haskell dependencies` \
diff --git a/build/docker/ubuntu-trusty/Dockerfile b/build/docker/ubuntu-trusty/Dockerfile
index 40f9c55..a8e4d3b 100644
--- a/build/docker/ubuntu-trusty/Dockerfile
+++ b/build/docker/ubuntu-trusty/Dockerfile
@@ -113,9 +113,15 @@
 `# GlibC dependencies` \
       libglib2.0-dev
 
-RUN apt-get install -y --no-install-recommends \
-`# golang (go) dependencies` \
-      golang-go
+# golang
+ENV GOLANG_VERSION 1.7.6
+ENV GOLANG_DOWNLOAD_URL https://golang.org/dl/go$GOLANG_VERSION.linux-amd64.tar.gz
+ENV GOLANG_DOWNLOAD_SHA256 ad5808bf42b014c22dd7646458f631385003049ded0bb6af2efc7f1f79fa29ea
+RUN curl -fsSL "$GOLANG_DOWNLOAD_URL" -o golang.tar.gz && \
+      echo "$GOLANG_DOWNLOAD_SHA256  golang.tar.gz" | sha256sum -c - && \
+      tar -C /usr/local -xzf golang.tar.gz && \
+      ln -s /usr/local/go/bin/go /usr/local/bin && \
+      rm golang.tar.gz
 
 RUN apt-get install -y --no-install-recommends \
 `# Haskell dependencies` \
diff --git a/build/docker/ubuntu-xenial/Dockerfile b/build/docker/ubuntu-xenial/Dockerfile
index b69d7ea..832542e 100644
--- a/build/docker/ubuntu-xenial/Dockerfile
+++ b/build/docker/ubuntu-xenial/Dockerfile
@@ -15,7 +15,9 @@
 # Using all stock Ubuntu Xenial packaging except for:
 # - d: does not come with Ubuntu so we're installing 2.073.2 for coverage
 # - dart: does not come with Ubuntu so we're installing 1.22.1 for coverage
-# - nodejs: Ubuntu comes with 4.2.6 which exits LTS April 2018, so we're installing 6.x
+# - dotnet: does not come with Ubuntu
+# - go: Xenial comes with 1.6, but we need 1.7 or later
+# - nodejs: Xenial comes with 4.2.6 which exits LTS April 2018, so we're installing 6.x
 #
 
 FROM buildpack-deps:xenial-scm
@@ -138,10 +140,15 @@
 `# GlibC dependencies` \
       libglib2.0-dev
 
-RUN apt-get install -y --no-install-recommends \
-`# golang (go) dependencies` \
-      golang-go \
-      golang-race-detector-runtime
+# golang
+ENV GOLANG_VERSION 1.7.6
+ENV GOLANG_DOWNLOAD_URL https://golang.org/dl/go$GOLANG_VERSION.linux-amd64.tar.gz
+ENV GOLANG_DOWNLOAD_SHA256 ad5808bf42b014c22dd7646458f631385003049ded0bb6af2efc7f1f79fa29ea
+RUN curl -fsSL "$GOLANG_DOWNLOAD_URL" -o golang.tar.gz && \
+      echo "$GOLANG_DOWNLOAD_SHA256  golang.tar.gz" | sha256sum -c - && \
+      tar -C /usr/local -xzf golang.tar.gz && \
+      ln -s /usr/local/go/bin/go /usr/local/bin && \
+      rm golang.tar.gz
 
 RUN apt-get install -y --no-install-recommends \
 `# Haskell dependencies` \