HPCC-10131: Add support for optional 'jvmlibpath' property in environment.conf; add additional error checking to JVM initialization.

1) The java.class.path parameter mistakenly receives an empty directory value if CLASSPATH isn't set in the environment. This manifests as a ':' prepended to the -Djava.class.path=xxx option passed to the JVM.

2) An exception should be thrown if the JVM cannot be initialized.

3) Add support for optional 'jvmlibpath' to environment.conf to explicitly support the -Djava.library.path=xxx option for the JVM.