HTTPProxy: some routes are ignored when they differ only on header condition operator or value

[skriss]

What steps did you take and what happened:
Define an HTTPProxy with several routes that all have the same prefix and all have a condition on the same header, but different operators or values (some examples below).

Observe that Envoy is only configured with the last route; the other ones are dropped.

# two routes that both have a 'contains' condition on the
# same header, with two different values.
apiVersion: projectcontour.io/v1
kind: HTTPProxy
metadata:
  name: dropped-routes-1
spec:
  virtualhost:
    fqdn: stevek.com
  routes:
    - conditions:
        - header:
            name: x-stevek
            contains: foo
      services:
        - name: svc1
          port: 80
    - conditions:
        - header:
            name: x-stevek
            contains: bar
      services:
        - name: svc2
          port: 80
---
# two routes that both have a condition on the
# same header -- one using 'contains' and one
# using 'notcontains'.
apiVersion: projectcontour.io/v1
kind: HTTPProxy
metadata:
  name: dropped-routes
spec:
  virtualhost:
    fqdn: stevek.com
  routes:
    - conditions:
        - header:
            name: x-stevek
            contains: foo
      services:
        - name: svc1
          port: 80
    - conditions:
        - header:
            name: x-stevek
            notcontains: foo
      services:
        - name: svc2
          port: 80

What did you expect to happen:
All of the routes to be configured with Envoy.

[skriss]

Looks like this is caused by this HeaderCondition method, which is used as part of a map key in this code.

I'm working on a fix + tests.