Migrate slot ID of client certs in network configuration.
If a network was configured with a client certificate before R38, the slot ID will either be missing or not be valid in R38 and later because of the added device wide token.
This migration code will look up a configured client certificate by its PKCS#11 ID and update the slot id.
If the certificate can't be found, the client configuration will be removed in order to trigger a clean 'missing configuration' error in the UI.
This change is primarily targeted for manually configured networks and not policy-configured networks. The latter are automatically updated by the chromeos::ClientCertResolver.
BUG=403900
Review URL: https://codereview.chromium.org/
471183002
Cr-Commit-Position: refs/heads/master@{#290044}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@290044 0039d316-1c4b-4281-b951-d872f2087c98