remove testng from gradle
Merge branch 'master' of https://github.com/0xdata/h2o-dev
Replace TestNG with JUnit

Reason: TestNG does not support critical debugging functionality (ability to
run groups of tests from the command line, which directly impacts dev ability
to discover which combo of tests triggered the failure).  Also observed TestNG
buffering all test output, which when 1 test hangs means no output - and so no
easy way to tell which test triggers the hang.

One-time all devs should run "gradle make" - which will pull libs locally.
Each time a new lib is added, this will have to be run once.

Pre-push all devs should run "make check" - which builds 5 real JVMs and tests
on them.  This is a strictly stronger test than "build 5 fake jvms in 1 real
jvm using classloaders", and is *required* pre-push.  Currently not available
from "gradle test" and I'm planning on fixing this pronto.  Meanwhile, use
"make check".  Also "make" and "make clean" work as expected.

"make check" will pick up new tests in the test dirs by default.

"gradle make" "gradle build" "gradle clean" should all work as expected.
"gradle test" does not work, and is being worked on.

Tool-chain requirement: pre-push tests run all JVMs from a standard shell, and
not from a JVM (such as Gradle) - so that the launch line for the crashing JVMs
is directly available for cut-n-paste operations into other debugging tools.