Class Install errors for jar lookup should include invalid path rather than string "BYTEMAN_HOME"

Class Install uses first system property org.jboss.byteman.home and then env var BYTEMAN_HOME to identify the location of the byteman agent jar, finally resorting to searching the classpath. If either of the first two settings identifies an invalid path Install prints an error and exits with a failure code.

The error messages currently report that BYTEMAN_HOME should be set to a valid path or include a valid lib dir and jar. This is true even if the path being searched was identified using the system property which is i) confusing and ii) fails to identify the invalid path.

The messages should be modified to report that the path itself is invalid and shoud not refer to its provenance via the env var or system property.