krb5 security, bug fix, and enhancement update

[1.15.1-18]

• Expose context errors in pkinit_server_plugin_init
• Resolves: #1460089
  [1.15.1-17]
• Drop certauth test changes that prevented runnig it
• Resolves: #1498767
  [1.15.1-16]
• Drop irrelevant DIR trigger logic
• Resolves: #1431198
  [1.15.1-15]
• Fix CVE-2017-7562 (certauth eku bypass)
• Resolves: #1498767
  [1.15.1-14]
• Fix CVE-2017-11368 (s4u2 request assertion failures)
• Resolves: #1498768
  [1.15.1-13]
• Force-add /etc/krb5.conf.d so we can guarantee it exists
• Resolves: #1431198
  [1.15.1-12]
• Add krb5 policy plugin interface
• Remove soname downgrade
• Resolves: #1462982
  [1.15.1-11]
• Make t_certauth.py runnable
• Resolves: #1443388
  [1.15.1-10]
• Add context SSF query support
• Resolves: #1472956
  [1.15.1-9]
• Remove incomplete PKINIT OCSP support
• Resolves: #1460089