RFR[XS] 8188105 Make -Xshare:auto the default for server VM

[Ioi Lam]

Hi, please review this very simple change:

https://bugs.openjdk.java.net/browse/JDK-8188105
http://cr.openjdk.java.net/~iklam/jdk11/8188105-make-xshare-auto-the-default.v01/

Summary:

Now the server VM will automatically load the CDS archive if one exists.
This has been the default for the client VM for many releases. It
was previously disabled for the server VM due to performance issues that
have since been fixed (in JDK-8074345).

Testing:

I have run hs-tier{1,2,3,4} with no failures.

Thanks
- Ioi