This commit adds a Samba4 test fixture that acts as a domain controller
and has the same contents as the cloud active directory instance that
we previously used for tests.
The tests also support reading information from environment variables
so that they can be run against a real active directory instance in our
CI builds.
In addition, this commit also fixes a few issues that surfaced when
making this change. The first is a change in the base DN that is
searched when performing down-level authentication. The base DN is
now the configuration object instead of the domain DN. This change was
required due to the original producing unnecessary referrals, which we
cannot easily follow when running against this test figure. Referrals
cannot easily be followed as they are returned by the ldap server with
an unresolvable DNS name unless the host points to the samba4 instance
for DNS. The port returned in the referral url is the one samba is bound
to, which differs from the port that is forwarded to the host by the
test fixture.
The other issue that is resolved by this change is the addition of
settings that allow specifying non-standard ports for active directory.
This is needed for down-level authentication as we may need to query
the regular port of active directory instead of the global catalog
port as the configuration object is not replicated to the global
catalog.
relates elastic/x-pack-elasticsearch#185
Relates elastic/x-pack-elasticsearch#3800
Original commit: elastic/x-pack-elasticsearch@883c742fba
bccf988e9d