RFR 8161291: Serialization Tests for URLPermission is failing

[Vyom Tewari]

Hi,

Please review the below code change.
Bug        : JDK-8161291  Serialization Tests for URLPermission is failing

Webrev  : 
http://cr.openjdk.java.net/~vtewari/8161291/webrev0.0/index.html 
<http://cr.openjdk.java.net/%7Evtewari/8161291/webrev0.0/index.html>

This change make sure that colon separator need to be present even if 
the request headers list is empty.

Thanks,

Vyom