[FIXED JENKINS-22368] Discovery fails behind proxy

This commit addresses the problem described in [FIXED JENKINS-22368] and
may also correct [JENKINS-11753]. Proxy settings in openid4java's
HttpClientFactory will now be initialized when calling the constructor of
the OpenIdSsoSecurityRealm & GoogleAppSsoSecurityRealm classes in addition
to the existing call in the commenceLogin process.