Description of problem:
===
GitLabIdentityProvider doesn't take care of "ca:" field.

Version-Release number of selected component (if applicable):
===
OCP 3.3.1.5-1

How reproducible(Steps to Reproduce):
===
step-1. Configure GitLabIdentityProvider as below:

  ---
  oauthConfig:
    assetPublicURL: https://foo.example.com:8443/console/
    grantConfig:
      method: auto
    identityProviders:
    - challenge: false
      login: true
      mappingMethod: claim
      name: gitlab_auth
      provider:
        apiVersion: v1
        ca: /path/to/ca-bundle.crt
        clientID: xxxx
        clientSecret: xxxx
        kind: GitLabIdentityProvider
        url: https://gitlab.foo.example.com
  ---

step-2. Login

Actual results:
===
Failed to login with following error:

  Dec  5 04:34:44 ip-172-31-193-103 atomic-openshift-master-api: E1205 04:34:44.549405  121009 errorpage.go:30] AuthenticationError: Get https://git.foo.example.com/api/v3/user: x509: certificate signed by unknown authority

Expected results:
===
Login successfully

Additional info:
===
We confirmed that the ca.crt and ca-bundle.crt worked:

   $ curl --cacert /path/to/ca-bundle.crt https://git.foo.example.com
   $ curl --cacert /path/to/ca.crt https://git.foo.example.com

Also, after removing "ca: /path/to/ca-bundle.crt" from GitLabIdentityProvider, if we include the ca.crt into root cas, it the login worked well.

  # update-ca-trust enable
  # cp /path/to/ca.crt /etc/pki/ca-trust/source/anchors/
  # update-ca-trust extract

From this, most probably GitLabIdentityProvider doesn't take care of ca: field.