FreeIPA's ipasam module to Samba uses gethostname() call to identify
own server's host name. This value is then used in multiple places,
including construction of cifs/host.name principal. ipasam module
always uses GSSAPI authentication when talking to LDAP, so Kerberos
keys must be available in the /etc/samba/samba.keytab. However, if
the principal was created using non-FQDN name but system reports
FQDN name, ipasam will fail to acquire Kerberos credentials.
Same with FQDN principal and non-FQDN hostname.

Also host name and principal name must have the same case.

Report an error when configuring ADTrust instance with inconsistent
runtime hostname and configuration. This prevents errors like this:

[20/21]: starting CIFS services
ipa         : CRITICAL CIFS services failed to start

where samba logs have this:

[2017/03/20 06:34:27.385307,  0] ipa_sam.c:4193(bind_callback_cleanup)
  kerberos error: code=-1765328203, message=Keytab contains no suitable keys for cifs/ipatrust@EXAMPLE.COM
[2017/03/20 06:34:27.385476,  1] ../source3/lib/smbldap.c:1206(get_cached_ldap_connect)
  Connection to LDAP server failed for the 16 try!