ci.sh: control which target is run for each of the configurations

There are two important things here:
* We only want to run "jdk-test" if we were running "test" for everything else.
  This gets around a bug where jdk-test fails for cross-compile builds (where JNI is involved)
* We can specify a different test target by setting the "test" environment variable.
  This is useful for cross-compiling the tests in a docker image
  (setting the test_target to "build-test")