dnspython: Add compatibility shim

`dnspython` 2.0.0 has many changes and several deprecations like:

```
> dns.resolver.resolve() has been added, allowing control of whether
search lists are used. dns.resolver.query() is retained for backwards
compatibility, but deprecated. The default for search list behavior can
be set at in the resolver object with the use_search_by_default
parameter. The default is False.

> dns.resolver.resolve_address() has been added, allowing easy
address-to-name lookups.
```

The new class `DNSResolver`:
- provides the compatibility layer
- defaults the previous behavior (the search list configured in the
  system's resolver configuration is used for relative names)
- defaults lifetime to 15sec (determines the number of seconds
  to spend trying to get an answer to the question)

Fixes: https://pagure.io/freeipa/issue/8383
Signed-off-by: Stanislav Levin <slev@altlinux.org>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>

ipaserver/install/installutils.py

@@ -38,7 +38,7 @@ from contextlib import contextmanager
 from configparser import ConfigParser as SafeConfigParser
 from configparser import NoOptionError
 
-from dns import resolver, rdatatype
+from dns import rdatatype
 from dns.exception import DNSException
 import ldap
 import six
@@ -53,6 +53,7 @@ from ipalib.constants import MAXHOSTNAMELEN
 from ipalib.util import validate_hostname
 from ipalib import api, errors, x509
 from ipapython.dn import DN
+from ipapython.dnsutil import resolve, get_ipa_resolver
 from ipaserver.install import certs, service, sysupgrade
 from ipaplatform import services
 from ipaplatform.paths import paths
@@ -187,7 +188,7 @@ def verify_fqdn(host_name, no_host_dns=False, local_hostname=True):
     # Verify this is NOT a CNAME
     try:
         logger.debug('Check if %s is not a CNAME', host_name)
-        resolver.query(host_name, rdatatype.CNAME)
+        resolve(host_name, rdatatype.CNAME)
         raise HostReverseLookupError("The IPA Server Hostname cannot be a CNAME, only A and AAAA names are allowed.")
     except DNSException:
         pass
@@ -284,11 +285,13 @@ def read_ip_addresses():
 def read_dns_forwarders():
     addrs = []
     if ipautil.user_input("Do you want to configure DNS forwarders?", True):
-        print("Following DNS servers are configured in /etc/resolv.conf: %s" %
-                ", ".join(resolver.get_default_resolver().nameservers))
+        print(
+            "Following DNS servers are configured in /etc/resolv.conf: %s"
+            % ", ".join(get_ipa_resolver().nameservers)
+        )
         if ipautil.user_input("Do you want to configure these servers as DNS "
                 "forwarders?", True):
-            addrs = resolver.default_resolver.nameservers[:]
+            addrs = get_ipa_resolver().nameservers[:]
             print("All DNS servers from /etc/resolv.conf were added. You can "
                   "enter additional addresses now:")
         while True: