RFR: 8279997: check_for_dynamic_dump should not exit vm

[Yumin Qi]

Hi, please review
  When run with -Xshare:auto and the base archive could not be loaded, vm should not exit in DynamicArchive::check_for_dynamic_dump, instead, it should continue without sharing.
  The fix is the run will continue but print out warning to remind user of using -Xlog:cds for more information.

Tests: tier1,tier4

Thanks
Yumin

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Commit messages:
 - 8279997: check_for_dynamic_dump should not exit vm

Changes: https://git.openjdk.java.net/jdk/pull/7433/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7433&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8279997
  Stats: 75 lines in 4 files changed: 38 ins; 15 del; 22 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7433.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7433/head:pull/7433

PR: https://git.openjdk.java.net/jdk/pull/7433