RFR: 8209837: Avoid initializing ExpiringCache during bootstrap

[Claes Redestad]

Hi,

it's a tiny startup improvement to rearrange code so that the 
ExpiringCaches used in the FileSystem implementations aren't created if 
they aren't going to be used:

Webrev: http://cr.openjdk.java.net/~redestad/8209837/open.00/

Bug: https://bugs.openjdk.java.net/browse/JDK-8209837

3 fewer classes loaded on bootstrap.

Thanks!

/Claes