Simplify test skipping

Change-Id: I45ca4998e50f60849f6f44544f3c8d22f33ac91c
diff --git a/t/script/serial.t b/t/script/serial.t
index ab71634..a4a64f1 100644
--- a/t/script/serial.t
+++ b/t/script/serial.t
@@ -6,6 +6,10 @@
 use File::Spec::Functions qw/catdir catfile/;
 use File::Temp qw/:POSIX/;
 
+if ($ENV{SKIP_SCRIPT}) {
+  plan skip_all => 'Skip script tests';
+};
+
 my $f = dirname(__FILE__);
 my $script = catfile($f, '..', '..', 'script', 'korapxml2krill');