Description of problem:
Builds fail when git clone must go through an HTTP proxy

Version-Release number of selected component (if applicable):
openshift-3.0.0.1-1.git.4.eab4c86.el7ose.x86_64

How reproducible:
Always

Steps to Reproduce:
1. Have an OpenShift environment where external connectivity must go through an HTTP proxy
2. Create a buildConfig with env vars for proxy settings:
      ...
        "strategy": {
          "sourceStrategy": {
            "env": [
              {
                "Value": "http://proxy.example.com:3128",
                "Name": "HTTP_PROXY"
              },
              {
                "Value": "http://proxy.example.com:3128",
                "Name": "HTTPS_PROXY"
              }
            ],
      ...
3. Start a build based on that bc

Actual results:

build fails with a message similar to:

I0715 07:36:46.402317       1 sti.go:84] Starting S2I build from 2000/ruby-hello-world-1 BuildConfig ...
I0715 07:36:46.402336       1 sti.go:112] Building 172.30.143.219:5000/2000/ruby-hello-world
I0715 07:36:46.412553       1 clone.go:26] Cloning into /tmp/sti871880716/upload/src
E0715 07:38:54.096969       1 git.go:102] fatal: unable to access 'https://github.com/openshift/ruby-hello-world/';: Failed connect to github.com:443; Connection timed out
I0715 07:38:54.097442       1 clone.go:28] Git clone failed: exit status 128

Expected results:

build succeeds

Additional info:
It seems that this was fixed in upstream issue 3395, https://github.com/openshift/origin/pull/3401 but apparently that's not in OSE code yet.

In other words: this BZ is a request to backport [the relevant parts of?] commit 64d3312