Description of problem:
Once a route is created, it cannot be updated to add a certificate (and therefore secure the route) by anything less than a cluster-admin. The error returned is:

An error occurred updating route test. Reason: Route "test" is invalid: spec.tls: Invalid value: route.TLSConfig{Termination:"edge", Certificate:"-----BEGIN CERTIFICATE-----\n...\n-----END CERTIFICATE-----", Key:"-----BEGIN CERTIFICATE-----\n...\n-----END CERTIFICATE-----", CACertificate:"-----BEGIN CERTIFICATE-----\n...\n-----END CERTIFICATE-----", DestinationCACertificate:"", InsecureEdgeTerminationPolicy:""}: field is immutable


Version-Release number of selected component (if applicable):
3.6

How reproducible:
100%

Steps to Reproduce:
1. create an app with a route
2. edit the route to secure and add certificates


Actual results:
An error occurred updating route test. Reason: Route "test" is invalid: spec.tls: Invalid value: route.TLSConfig{Termination:"edge", Certificate:"-----BEGIN CERTIFICATE-----\n...\n-----END CERTIFICATE-----", Key:"-----BEGIN CERTIFICATE-----\n...\n-----END CERTIFICATE-----", CACertificate:"-----BEGIN CERTIFICATE-----\n...\n-----END CERTIFICATE-----", DestinationCACertificate:"", InsecureEdgeTerminationPolicy:""}: field is immutable


Expected results:
Route updated successfully

Additional info:
Similar to bz:
https://bugzilla.redhat.com/show_bug.cgi?id=1524707