warn on missing service cert signer in oadm diagnostics

[deads2k]

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=1501952

Updates master-config.yaml validation to warn on missing service serving signer cert configuration.

@mrobson

[deads@deads-02 origin]$ oc adm diagnostics --master-config=openshift.local.config/master/master-config.yaml MasterConfigCheck
[Note] Determining if client configuration exists for client/cluster diagnostics
Info:  Successfully read a client config file at '/home/deads/.kube/config'
[Note] Performing systemd discovery

[Note] Running diagnostic: MasterConfigCheck
       Description: Check the master config file
       
WARN:  [DH0005 from diagnostic MasterConfigCheck@openshift/origin/pkg/diagnostics/host/check_master_config.go:52]
       Validation of master config file 'openshift.local.config/master/master-config.yaml' warned:
       assetConfig.loggingPublicURL: Invalid value: "": required to view aggregated container logs in the console
       assetConfig.metricsPublicURL: Invalid value: "": required to view cluster metrics in the console
       controllerConfig.serviceServingCert.signer: Required value: required for the service serving cert signer; automatic serving certificate signing will fail
       
[Note] Summary of diagnostics execution (version v3.7.0-alpha.1+05f812f-1107-dirty):
[Note] Warnings seen: 1

[deads2k]

/retest

[deads2k]

/retest
/assign mrobson
/assign soltysh

[mrobson]

/lgtm

[openshift-merge-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: deads2k, mrobson

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[mrobson]

/retest

[soltysh]

This seems reasonable to land in 3.7

/retest
/kind bug

[deads2k]

/retest

[deads2k]

/retest

[deads2k]

/retest

[deads2k]

/retest

[soltysh]

/retest

[openshift-bot]

/retest

Please review the full test history for this PR and help us cut down flakes.

[openshift-merge-robot]

/test all [submit-queue is verifying that this PR is safe to merge]

[openshift-merge-robot]

Automatic merge from submit-queue (batch tested with PRs 16943, 16872, 16916, 16863, 16925).

[openshift-ci-robot]

@deads2k: The following test failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
ci/openshift-jenkins/extended_conformance_gce	d8b6baa	link	/test extended_conformance_gce

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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