Do not check if port 8443 is available in step 2 of external CA install

The port is never available in step 2 of external CA install, as Dogtag is
already running.

https://fedorahosted.org/freeipa/ticket/4660

Reviewed-By: David Kupka <dkupka@redhat.com>

install/tools/ipa-ca-install

@@ -280,6 +280,7 @@ def install_master(safe_options, options):
     domain_name = api.env.domain
     host_name = api.env.host
 
+    if external != 2:
         check_ca()
 
     dirname = dsinstance.config_dirname(

install/tools/ipa-server-install

@@ -886,7 +886,8 @@ def main():
 
         if setup_ca:
             if not cainstance.check_port():
-            print "IPA requires port 8443 for PKI but it is currently in use."
+                print ("IPA requires port 8443 for PKI but it is currently in "
+                       "use.")
                 sys.exit("Aborting installation")
 
     if options.conf_ntp: