CLOUDSTACK-4810: Enable hypervisor snapshots for CloudStack-managed storage (for XenServer and VMware)
few cleanups in CertServiceTest and CertService

Tests:
- all tests are @Test rather than having one test to call them, so they can be run one by one
- tests that expect exception from a method fail if there is none
- no longer extends TestCase so that the original method names could be kept as test

Implementation:
- include root cause in exceptions when possible - helps at troubleshuting
- close readers

Signed-off-by: Laszlo Hornyak <laszlo.hornyak@gmail.com>
Add assumtion on OpenJDK for tests that build on JCE

This patch adds an assumption that OpenJDK is used in some of the tests.
OpenJDK detection utility also added. By specifying -Dcloudstack.jce.enabled=true in the test parameters the OpenJDK detection can be overridden.

Signed-off-by: Laszlo Hornyak <laszlo.hornyak@gmail.com>