To make configuration easier the IPA subdomain provider should be always
loaded if the IPA ID provider is configured and the subdomain provider
is not explicitly disabled. But to avoid the overhead of regular
subdomain requests in setups where no subdomains are used the IPA
subdomain provider should behave differently if configured explicit or
implicit.
If the IPA subdomain provider is configured explicitly, i.e.
'subdomains_provider = ipa' can be found in the domain section of
sssd.conf subdomain request are always send to the server if needed.
If it is configured implicitly and a request to the server fails
with an indication that the server currently does not support subdomains
at all, e.g. is not configured to handle trust relationships, a new
request will be only send to the server after a long timeout or after
a going-online event.
To be able to make this distinction this patch save the configuration
status to the subdomain context.
Fixes https://fedorahosted.org/sssd/ticket/1613