RFR: 8191808: Configurable read timeout for CRLs

[Sean Mullan]

Please review this change to add a system property for configuring the 
read timeout when downloading CRLs with a default value of 15 seconds. 
Currently there is no timeout so downloads of large CRLs can block for a 
long time or indefinitely. Current workaround is to use the 
sun.net.client.defaultReadTimeout system property but that affects all 
connections.

bug: https://bugs.openjdk.java.net/browse/JDK-8191808
CSR: https://bugs.openjdk.java.net/browse/JDK-8223310
webrev: http://cr.openjdk.java.net/~mullan/webrevs/8191808/webrev.00/

Thanks,
Sean