Improve ClassLoaderUtils.loadClassWithTCCL()

Improve ClassLoaderUtils.loadClassWithTCCL()

There are scenarios when we do not have a Thread Context Class Loader,
such as when executing from Netty's GlobalEventExecutor. When we attempt
to load a class in that scenario, the method will throw a NPE, which
exposes users which can deal with the class not being able to load
to a RuntimeException -- preventing recovery.

Detect the case when TCCL is null and report a failure to load the class,
noting the reason for the failure.

Change-Id: Ia6837ba451d290a2070bc24e9e7088c60275cae0
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>