Added SKIP_MIGRATION option.
Added SKIP_MIGRATION option.

The option skips migration when system envrionment is set to truthy
and TESTING is True.

dominikkowalski/django-powerdns-dnssec,dominikkowalski/django-powerdns-dnssec,dominikkowalski/django-powerdns-dnssec,allegro/django-powerdns-dnssec,allegro/django-powerdns-dnssec,dominikkowalski/django-powerdns-dnssec,allegro/django-powerdns-dnssec,allegro/django-powerdns-dnssec,dominikkowalski/django-powerdns-dnssec