Correct handling of -s switch.

misc-scripts/production_database/scripts/update_database_list.pl

@@ -74,7 +74,7 @@ ABOUT_END
 }
 
 my $release;
-my @servers = ( 'ens-staging1', 'ens-staging2' );
+my @servers;
 my $master = 'ens-staging1';
 
 my $dbport = '3306';
@@ -107,6 +107,10 @@ if ( !GetOptions( 'release|r=s'  => \$release,
   exit();
 }
 
+if ( !@servers ) {
+  @servers = ( 'ens-staging1', 'ens-staging2' );
+}
+
 my %species;
 my %databases;