Description of problem:
a https readiness endpoint is considered invalid if httpsProxy uses a http url scheme. httpsProxy supports http and https url schemes. It's common to use an http url scheme for an https proxy. Cluster Network Operator should consider either httpsProxy url scheme valid when using a readiness endpoint with an https scheme.

Version-Release number of selected component (if applicable):
version: 4.2.0-0.okd-2019-09-09-195703

How reproducible:
Always

Steps to Reproduce:
1. Create a cluster without proxy enabled, but with additionalTrustBundle configured with your proxy's trust bundle.
2. Enable proxy by configuring a http url scheme for httpsProxy and a readiness endpoint with a https scheme. For example:

$ oc get proxy/cluster -o yaml
apiVersion: config.openshift.io/v1
kind: Proxy
metadata:
  creationTimestamp: "2019-09-09T20:39:41Z"
  generation: 7
  name: cluster
  resourceVersion: "441834"
  selfLink: /apis/config.openshift.io/v1/proxies/cluster
  uid: f2bddab5-d341-11e9-85b7-0280d2574602
spec:
  httpProxy: http://<user>:<psswd>@<http_proxy>:<httpProxy_port>
  httpsProxy: http://<user>:<psswd>@<https_proxy>:<httpsProxy_port>
  readinessEndpoints:
  - http://www.google.com
  - https://www.google.com
  trustedCA:
    name: user-ca-bundle
<SNIP>

3. View the proxy and notice that status is not being set.
oc get proxy/cluster -o yaml

4. View the network operator
oc get clusteroperator/network -o yaml

Actual results:
message: 'The configuration is invalid for proxy ''cluster'' (readinessEndpoint
      probe failed for endpoint ''https://www.google.com'': endpoint ''https://www.google.com''requires a `https` proxy scheme). Use ''oc edit proxy.config.openshift.io cluster'' to fix.'

Expected results:

cluster-network-operator to accept the configuration and write spec > status.

Additional info: