RFR(XS) 8233446: Improve error handling when specified dynamic archive doesn't exist

[Ioi Lam]

https://bugs.openjdk.java.net/browse/JDK-8233446
http://cr.openjdk.java.net/~iklam/jdk14/8233446-error-handling-when-dyn-archive-not-found.v01/

With this patch, error handling in CDS is the same when the static archive
or the dynamic archive cannot be opened at runtime:

-Xshare:auto (default)
     VM will continue to execute without mapping the specified but
     unavailable archive. (Same as before this patch)

-Xshare:on (deprecated)
     VM will exit with an error message


So this patch only modifies the behavior of -Xshare:on, which is deprecated
anyway. However, the code is simplified and more consistent, and will 
make it easier
to remove support for -Xshare:on in the future.

Tested with hs-tier1/hs-tier2

Thanks
- Ioi