RFR: 8207812: Implement Dynamic CDS Archive

[Calvin Cheung]

This is a follow-up on the preliminary code review sent by Jiangli in 
January[1].

Highlights of changes since then:
1. New vm option for dumping a dynamic archive 
(-XX:ArchiveClassesAtExit=<dynamic archive>) and enhancement to the 
existing -XX:SharedArchiveFile option. Please refer to the corresponding 
CSR[2] for details.
2. New way to run existing AppCDS tests in dynamic CDS archive mode. At 
the jtreg command line, the user can run many existing AppCDS tests in 
dynamic CDS archive mode by specifying the following:
     -vmoptions:-Dtest.dynamic.cds.archive=true 
<jdk>/open/test/hotspot/jtreg:hotspot_appcds_dynamic
    We will have a follow-up RFE to determine in which tier the above 
tests should be run.
3. Added more tests.
4. Various bug fixes to improve stability.

RFE: https://bugs.openjdk.java.net/browse/JDK-8207812
webrev: 
http://cr.openjdk.java.net/~ccheung/8207812_dynamic_cds_archive/webrev.00/

(The webrev is based on top of the following rev: 
http://hg.openjdk.java.net/jdk/jdk/rev/805584336738)

Testing:
     - mach5 tiers 1- 3 (including the new tests)
     - AppCDS tests in dynamic CDS archive mode on linux-x64 (a few 
tests require more investigation)

thanks,
Calvin

[1] 
https://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2019-January/032176.html
[2] https://bugs.openjdk.java.net/browse/JDK-8221706