CLDAP: do not read IPA domain from hostname

Currently the CLDAP plugin determines the IPA domain name by reading
the current host name and splitting of the domain part. But since an IPA
server does not have to be in a DNS domain which has the same name as
the IPA domain this may fail. The domain name was used to search the
ipaNTDomainAttrs object, but since this object is unique in the tree it
is sufficient to use the objectclass in the search filter. Now the IPA
domain can be read from the ipaNTDomainAttrs object as well.

Fixes https://fedorahosted.org/freeipa/ticket/3941
Ensure credentials structure is initialized

https://fedorahosted.org/freeipa/ticket/3953
Use correct super-calls in get_args() methods

The get_args methods in ipalib.crud and ipalib.plugins.baseldap used
super() calls that skipped some of the classes in the inheritance
chain, and contained code that reimplemented some of the skipped
functionality.
This made it difficult to customize the get_args behavior.

Use proper super() calls.
Fix enablement of automount map type selector

Map type radio used old way of defining that its value should not be used in add command.  Recent patch related to 'enable' attribute hardened/fixed the behavior of radio widgets so they are disabled in UI as well when enabled==false. Automount did not reflect this change.

https://fedorahosted.org/freeipa/ticket/3954
Do not add trust to AD in case of IPA realm-domain mismatch

Make sure that trust-add command fails when admin attempts
to add an Active Directory trust when the realm name and
the domain name of the IPA server do not match.

https://fedorahosted.org/freeipa/ticket/3923
Warn user about realm-domain mismatch in install scripts

If the IPA server is setup with non-matching domain and realm
names, it will not be able to estabilish trust with the Active
Directory.

Adds warnings to the ipa-server-install and warning to the
ipa-adtrust-install (which has to be confirmed).

Man pages for the ipa-server-install and ipa-adtrust-install were
updated with the relevant notes.

https://fedorahosted.org/freeipa/ticket/3924
Use FQDN when creating MSDCS SRV records

When IPA server hostname is outside of default DNS domain, instead
of relative domain name, FQDN should be used.

https://fedorahosted.org/freeipa/ticket/3908
Do not set DNS discovery domain in server mode

In server mode, the discovery domain should be left unset in all
cases as the DNS discovery is only driven by the AD domains.

https://fedorahosted.org/freeipa/ticket/3947
test_integration.host: Move transport-related functionality to a new module

This will make it possible to use a different mechanism for cases like
- Paramiko is not available
- Hosts without SSH servers (e.g. Windows)

Add BaseHost, Transport & Command base classes that define the interface
and common functionality, and Host, ParamikoTransport & SSHCommand with
specific details.

The {get,put}_file_contents methods are left on Host for convenience;
all other Transport methods must be now accessed through the transport.

Part of the work for https://fedorahosted.org/freeipa/ticket/3890
test_integration: Add OpenSSHTransport, used if paramiko is not available

This adds a transport that uses /usr/bin/ssh calls to communicate
with remote hosts.
This transport is a bit slower and buffers output more than paramiko,
so it is only used if paramiko is not available, or forced with an
environment variable.

https://fedorahosted.org/freeipa/ticket/3890