Expose context errors in pkinit_server_plugin_init

Expose context errors in pkinit_server_plugin_init

Commit 3ff426b9048a8024e5c175256c63cd0ad0572320 attempted to display
an error when OCSP support was requested, but this error message was
suppressed in pkinit_server_plugin_init().  Add a trace log for each
realm initialization error, and pass through the realm initialization
error when the KDC serves only one realm.  Other error messages from
pkinit_init_kdc_profile(), such as missing pkinit_identity or
pkinit_anchors, are also now exposted.

[ghudson@mit.edu: clarified commit message]

ticket: 8621 (new)
target_version: 1.16
tags: pullup