Default testset in JPRT should not run all tests

The default testset for control and jdk jobs includes following targets:

  65 jprt.make.rule.default.test.targets= \
  66 ${jprt.my.test.target.set:TESTNAME=langtools_jtreg}, \
  67 ${jprt.my.test.target.set:TESTNAME=jdk_beans1}, \
  68 ${jprt.my.test.target.set:TESTNAME=jdk_io}, \
  69 ${jprt.my.test.target.set:TESTNAME=jdk_lang}, \
  70 ${jprt.my.test.target.set:TESTNAME=jdk_math}, \
  71 ${jprt.my.test.target.set:TESTNAME=jdk_misc}, \
  72 ${jprt.my.test.target.set:TESTNAME=jdk_net}, \
  73 ${jprt.my.test.target.set:TESTNAME=jdk_nio1}, \
  74 ${jprt.my.test.target.set:TESTNAME=jdk_nio2}, \
  75 ${jprt.my.test.target.set:TESTNAME=jdk_nio3}, \
  76 ${jprt.my.test.target.set:TESTNAME=jdk_security1}, \
  77 ${jprt.my.test.target.set:TESTNAME=jdk_text}, \
  78 ${jprt.my.test.target.set:TESTNAME=jdk_util}

This is way too many to keep stable for everyone using JPRT. We should change the default to be:

  64 # Default jdk test targets (testset=default)
  65 jprt.make.rule.default.test.targets= \
  66 ${jprt.my.test.target.set:TESTNAME=langtools_jtreg}, \
  67 ${jprt.my.test.target.set:TESTNAME=jdk_lang}, \
  68 ${jprt.my.test.target.set:TESTNAME=jdk_math}

and introduce a new "core" testset for folks that want to run all tests except the client area.