installer: Fix logic of reading option values from cache.

Only options explicitly set must be stored before installer exits first step
of external CA setup. When installer continues all stored option values must
be restored.

https://fedorahosted.org/freeipa/ticket/5556

Reviewed-By: Jan Cholasta <jcholast@redhat.com>

ipaserver/install/server/install.py

@@ -444,9 +444,7 @@ def install_check(installer):
             sys.exit("Directory Manager password required")
         try:
             cache_vars = read_cache(dm_password)
-            for name, value in cache_vars.items():
-                if name not in options.__dict__:
-                    options.__dict__[name] = value
+            options.__dict__.update(cache_vars)
             if cache_vars.get('external_ca', False):
                 options.external_ca = False
                 options.interactive = False
@@ -867,7 +865,8 @@ def install(installer):
             options.admin_password = admin_password
             options.host_name = host_name
             options.reverse_zones = dns.reverse_zones
-            cache_vars = {n: getattr(options, n) for o, n in installer.knobs()}
+            cache_vars = {n: options.__dict__[n] for o, n in installer.knobs()
+                          if n in options.__dict__}
             write_cache(cache_vars)
 
         ca.install_step_0(False, None, options)