Mark some attributes required to match the schema.

This makes no changes to the functionality in the command-line or
GUI because these all have defaults anyway. This is mostly to show
them properly in the UI and prevent someone from trying to erase the
value (and getting a nasty schema error in response).

https://fedorahosted.org/freeipa/ticket/2015

ipalib/plugins/dns.py

@@ -673,7 +673,7 @@ class dnszone(LDAPObject):
             default_from=lambda idnsname: 'hostmaster.%s' % idnsname,
             normalizer=normalize_zonemgr,
         ),
-        Int('idnssoaserial?',
+        Int('idnssoaserial',
             cli_name='serial',
             label=_('SOA serial'),
             doc=_('SOA record serial number'),
@@ -681,7 +681,7 @@ class dnszone(LDAPObject):
             create_default=_create_zone_serial,
             autofill=True,
         ),
-        Int('idnssoarefresh?',
+        Int('idnssoarefresh',
             cli_name='refresh',
             label=_('SOA refresh'),
             doc=_('SOA record refresh time'),
@@ -689,7 +689,7 @@ class dnszone(LDAPObject):
             default=3600,
             autofill=True,
         ),
-        Int('idnssoaretry?',
+        Int('idnssoaretry',
             cli_name='retry',
             label=_('SOA retry'),
             doc=_('SOA record retry time'),
@@ -697,7 +697,7 @@ class dnszone(LDAPObject):
             default=900,
             autofill=True,
         ),
-        Int('idnssoaexpire?',
+        Int('idnssoaexpire',
             cli_name='expire',
             label=_('SOA expire'),
             doc=_('SOA record expire time'),
@@ -705,7 +705,7 @@ class dnszone(LDAPObject):
             minvalue=0,
             autofill=True,
         ),
-        Int('idnssoaminimum?',
+        Int('idnssoaminimum',
             cli_name='minimum',
             label=_('SOA minimum'),
             doc=_('How long should negative responses be cached'),