service installers: clean up the inheritance

Instead of delegating handling of some parameters like fstore to the parent
class, the *Instance installers had the logic copy-pasted in their
constructors. Some other members were also moved to the Service class and the
parent class constructors in children were fixed to modern standards of
initializing parent class in Python.

https://fedorahosted.org/freeipa/ticket/6392

Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>

ipaserver/install/krbinstance.py

@@ -28,7 +28,6 @@ import dns.name
 
 from ipaserver.install import service
 from ipaserver.install import installutils
-from ipapython import sysrestore
 from ipapython import ipautil
 from ipapython import kernel_keyring
 from ipalib.constants import CACERT
@@ -50,7 +49,11 @@ class KpasswdInstance(service.SimpleServiceInstance):
 
 class KrbInstance(service.Service):
     def __init__(self, fstore=None):
-        service.Service.__init__(self, "krb5kdc", service_desc="Kerberos KDC")
+        super(KrbInstance, self).__init__(
+            "krb5kdc",
+            service_desc="Kerberos KDC",
+            fstore=fstore
+        )
         self.fqdn = None
         self.realm = None
         self.domain = None
@@ -63,11 +66,6 @@ class KrbInstance(service.Service):
         self.sub_dict = None
         self.pkcs12_info = None
 
-        if fstore:
-            self.fstore = fstore
-        else:
-            self.fstore = sysrestore.FileStore(paths.SYSRESTORE)
-
     suffix = ipautil.dn_attribute_property('_suffix')
     subject_base = ipautil.dn_attribute_property('_subject_base')