Adds $GOPATH/bin to PATH and reduces an extra layer from image

[navidshaikh]

Merges yum -y update layer with yum install golang layer.
Creates $GOPATH/src and $GOPATH/bin directories.
Appends $GOPATH/bin to $PATH env variable.
Uses $GOPATH as workdir instead of hard cording /go.

[mohammedzee1000]

LGTM

[navidshaikh]

Additional information on the built image (manual build).
Layers - 2

✗ docker inspect -f {{.RootFS.Layers}} centos7-golang                      
[sha256:e15afa4858b655f8a5da4c4a41e05b908229f6fab8543434db79207478511ff7 sha256:201701adb1122ff293cd4905dee9b4afcecd94bfc7ac1fef3e45fd07f804180f]

✗ docker run -ti centos7-golang
[root@9d427735caff go]# rpm -q golang
golang-1.8.3-1.el7.x86_64

[root@9d427735caff go]# echo $GOPATH
/go

[root@9d427735caff go]# echo $PATH  
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/go/bin

[root@9d427735caff go]# ll /go/
total 8
drwxrwxrwx. 2 root root 4096 Mar  1 08:46 bin
drwxrwxrwx. 2 root root 4096 Mar  1 08:46 src

[navidshaikh]

Removed installation of git RPM.
The centos golang image should have pure centos and golang stack, needed additional dependencies to be installed explicitly via application layers.

ping @mohammedzee1000

[dharmit]

golang package doesn't pull git as a dependency.

[navidshaikh]

golang package doesn't pull git as a dependency.

Thanks! git is needed in golang image for go get utility and golang package needs to add git as dependencies.

Updated the PR, reverted removing the installation of git RPM.