BZ449637:  when a farjar is run with a java agent, it unzips the wrong j...

...ar giving a NPE

retrieve jar name based on the class FatJarStarter instead of the class loader URL list

(this commit also changes the temp dir creation to use File instead of String operations
and fixes an issue where the jar couldn't be extracted if it was manipulated with jar
command, which apparently puts the dirs after the files on updates)

Signed-off-by: Alex <alexlehm@gmail.com>

ok, that doesn't work, it is necessary to cut off the string at the last !.
The class location returned by the getResource is something like
jar:file:/C:/Projects/vertx/agentissue/target/agentissue%20%5b!%5d.jar!/org/vertx/java/platform/impl/FatJarStarter.class
it includes the path of the class file inside the jar. This has to be cut off.