RFR(S): JDK-8222299: [TESTBUG] move hotspot container tests to hotspot/containers

[mikhailo.seledtsov at oracle.com]

Please review this change that moves HotSpot container tests into their 
own directory under test/hotspot/jtreg and
creates hotspot_containers test group. Since container tests require 
specially setup/configured environment, it is best to group them into 
their own group,
so they could be executed in properly configured environment. The 
details of this change, such as new location were
recommended by David and Igor during earlier public review for this 
issue (8222299: [TESTBUG] Docker tests should be excluded from 
hotspot_runtime group).

Also, as part of this review, Igor recommended to use jtreg.skipped 
exception if docker image build fails, which I agreed to
and implemented.

     JBS: https://bugs.openjdk.java.net/browse/JDK-8222299
     Webrev: http://cr.openjdk.java.net/~mseledtsov/8222299.00/
     Testing:
        Ran the affected tests on a machine configured for Docker testing.
        Ran them two ways, via specifying the directory as well as by 
using a newly created group - PASS


Thank you,
Misha