RFR(S): 8221342: [TESTBUG] Generate Dockerfile for docker testing

[mikhailo.seledtsov at oracle.com]

Please review this improvement to docker/container related testing in 
HotSpot and JDK.
This change came out of discussion for "8221221 make test 
TEST="jtreg:test/hotspot/jtreg/runtime/containers" failed on Ubuntu 
18.04". This fix is more generic, allowing to specify platform-specific 
docker base images, as well custom base images specified via test 
properties at test execution time. Also, it eliminates duplication 
(duplicate Dockerfile-xyz).

     JBS: https://bugs.openjdk.java.net/browse/JDK-8221342
     Webrev: http://cr.openjdk.java.net/~mseledtsov/8221342.01/
     Testing:
       rm -Rf JT*; jtreg -v1 
test/hotspot/jtreg/runtime/containers/docker/ 
jdk/jdk/internal/platform/docker/
       All PASS

       rm -Rf JT*; jtreg -v1 -Djdk.test.docker.image.name=ubuntu \
           -Djdk.test.docker.image.version=latest\
            test/hotspot/jtreg/runtime/containers/docker/ 
jdk/jdk/internal/platform/docker/
       All PASS
       Also ran the image interactively to make sure it is based on ubuntu


Thank you,

Misha