Expected at least one private key

[andre-perry-deidle]

When running the tests against a non-docker hydra (current master) I get the following:

=== RUN   TestManager/case=hydra
--- FAIL: TestManager (1.87s)
    --- PASS: TestManager/case=local (0.01s)
    --- FAIL: TestManager/case=hydra (1.86s)
        Error Trace:    manager_test.go:71
        Error:          Received unexpected error:
                        Expected at least one private key but got none
                        github.com/ory/oathkeeper/rsakey.(*HydraManager).Refresh
                                /home/andre/go2/src/github.com/ory/oathkeeper/rsakey/manager_hydra.go:68
                        github.com/ory/oathkeeper/rsakey.TestManager.func1
                                /home/andre/go2/src/github.com/ory/oathkeeper/rsakey/manager_test.go:71
                        testing.tRunner
                                /nix/store/d3vzj0lqdd879m812kpwzazzxzb27bik-go-1.10.1/share/go/src/testing/testing.go:777
                        runtime.goexit
                                /nix/store/d3vzj0lqdd879m812kpwzazzxzb27bik-go-1.10.1/share/go/src/runtime/asm_amd64.s:2361
        Test:           TestManager/case=hydra
FAIL
FAIL    github.com/ory/oathkeeper/rsakey        1.872s

It looks like there has been a change to generating the keys to use a GUID causing https://github.com/ory/oathkeeper/blob/master/rsakey/manager_hydra.go#L42 to not find it and loop generating initial RSA keys.

I hacked a fix by introducing a new key identifier. I see there are changes coming for hydra and was thinking of targeting the later code if possible.

[aeneasr]

This is fixed on master