ipareplica: ipareplica_setup_adtrust fails while updating ipaNTFlatName

The internal parameter sid_generation_always is generated in
ipareplica_test to enable SID generation if ipareplica_setup_adtrust is
not enabled.

This parameter was not used for ipareplica_prepare though, therefore
adtrust.install_check was not executed and did not set the attribute
adtrust.netbios_name. As a result adtrust.netbios_name was None and the
try to use this as the new NetBIOS domain name failed with an
INVALID_SYNTAX error in adtrustinstance while executing
ipareplica_setup_adtrust.

This issue only occurs if SIDs are not enabled in the domain yet for
example with an old deployment.