Use secure method to acquire IPA CA certificate

Major changes ipa-client-install:

* Use GSSAPI connection to LDAP server to download CA cert (now
  the default method)

* Add --ca-cert-file option to load the CA cert from a disk file.
  Validate the file. If this option is used the supplied CA cert
  is considered definitive.

* The insecure HTTP retrieval method is still supported but it must be
  explicitly forced and a warning will be emitted.

* Remain backward compatible with unattended case (except for aberrant
  condition when preexisting /etc/ipa/ca.crt differs from securely
  obtained CA cert, see below)

* If /etc/ipa/ca.crt CA cert preexists the validate it matches the
  securely acquired CA cert, if not:

  - If --unattended and not --force abort with error

  - If interactive query user to accept new CA cert, if not abort

  In either case warn user.

* If interactive and LDAP retrieval fails prompt user if they want to
  proceed with insecure HTTP method

* If not interactive and LDAP retrieval fails abort unless --force

* Backup preexisting /etc/ipa/ca.crt in FileStore prior to execution,
  if ipa-client-install fails it will be restored.

Other changes:

* Add new exception class CertificateInvalidError

* Add utility convert_ldap_error() to ipalib.ipautil

* Replace all hardcoded instances of /etc/ipa/ca.crt in
  ipa-client-install with CACERT constant (matches existing practice
  elsewhere).

* ipadiscovery no longer retrieves CA cert via HTTP.

* Handle LDAP minssf failures during discovery, treat failure to check
  ldap server as a warninbg in absebce of a provided CA certificate via
  --ca-cert-file or though existing /etc/ipa/ca.crt file.

Signed-off-by: Simo Sorce <simo@redhat.com>
Signed-off-by: Rob Crittenden <rcritten@redhat.com>

ipaserver/install/certs.py

@@ -227,7 +227,10 @@ class CertDB(object):
         if not subject_base:
             self.subject_base = DN(('O', 'IPA'))
 
-        self.cacert_name = get_ca_nickname(self.realm)
+        if self.self_signed_ca:
+            self.cacert_name = get_ca_nickname(self.realm, 'CN=%s Certificate Authority')
+        else:
+            self.cacert_name = get_ca_nickname(self.realm)
         self.valid_months = "120"
         self.keysize = "1024"