Use Go binary instead of building from source

Dockerfile

@@ -3,14 +3,14 @@ FROM ubuntu:14.04.1
 ## Environment setup
 ENV HOME /root
 ENV GOPATH /root/go
-ENV PATH /golang/bin:/root/go/bin:/usr/local/go/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
+ENV PATH /root/go/bin:/usr/local/go/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
 
 RUN mkdir -p /root/go
 ENV DEBIAN_FRONTEND noninteractive
 
 ## Install base dependencies
 RUN apt-get update && apt-get upgrade -y
-RUN apt-get install -y git mercurial build-essential software-properties-common pkg-config libgmp3-dev libreadline6-dev libpcre3-dev libpcre++-dev
+RUN apt-get install -y git mercurial build-essential software-properties-common wget pkg-config libgmp3-dev libreadline6-dev libpcre3-dev libpcre++-dev
 
 ## Install Qt5.4
 # RUN add-apt-repository ppa:beineri/opt-qt54-trusty -y
@@ -18,10 +18,9 @@ RUN apt-get install -y git mercurial build-essential software-properties-common
 # RUN apt-get install -y qt54quickcontrols qt54webengine mesa-common-dev libglu1-mesa-dev
 # ENV PKG_CONFIG_PATH /opt/qt54/lib/pkgconfig
 
-## Build and install latest Go
-RUN git clone https://go.googlesource.com/go golang
-RUN cd golang && git checkout go1.4.1
-RUN cd golang/src && ./make.bash && go version
+# Install Golang
+RUN wget https://storage.googleapis.com/golang/go1.4.1.linux-amd64.tar.gz
+RUN tar -C /usr/local -xzf go*.tar.gz && go version
 
 # this is a workaround, to make sure that docker's cache is invalidated whenever the git repo changes
 ADD https://api.github.com/repos/ethereum/go-ethereum/git/refs/heads/develop file_does_not_exist