ipabackup: Fix order of ipabackup_name parameter evaluation.

When performing a backup with 'state:present', if 'ipabackup_name' is
provided, the backup will be performed, but the role with return an
error since 'ipabackup_name' should not be set for this state.

This patch moves the parameter evaluation to be performed before the
actual backup is performed, so that the backup is not performed and an
error is reported.