Clear kernel keyring in client installer, save dbdir on new connections
This patch addresses two issues:
1. If a client is previously enrolled in an IPA server and the server
gets re-installed then the client machine may still have a keyring
entry for the old server. This can cause a redirect from the
session URI to the negotiate one. As a rule, always clear the keyring
when enrolling a new client.
2. We save the NSS dbdir in the connection so that when creating a new
session we can determine if we need to re-initialize NSS or not. Most
of the time we do not. The dbdir was not always being preserved between
connections which could cause an NSS_Shutdown() to happen which would
fail because of existing usage. This preserves the dbdir information when
a new connection is created as part of the session mechanism.
https://fedorahosted.org/freeipa/ticket/3108