check for installed dependencies when *not* in standalone mode

The condition that controls when to check for samba dependencies was
misformulated. The check should be run when the installer is *not* run
as standalone. In standalone mode the check is already made in different
place so the original code triggered it twice.

https://fedorahosted.org/freeipa/ticket/6630

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

ipaserver/install/adtrust.py

@@ -348,7 +348,7 @@ def install_check(standalone, options, api):
     global netbios_name
     global reset_netbios_name
 
-    if standalone:
+    if not standalone:
         check_for_installed_deps()
 
     realm_not_matching_domain = (api.env.domain.upper() != api.env.realm)