Ensure Weblogic and Websphere JMX are covered

To ensure an MBeanServer is available when needed you have to
look in JNDI before resorting to the JDK platform factory.

I had to copy some private code from Spring, but it seems
worth it.

Fixes gh-1092
Ignore test that is WIP
Re-instate test when fixed
Remove workaround for bug they fixed in Groovy
Polish
Allow prefixed bytes with fat JARs

Update `spring-boot-loader` ZIP processing code to support prefixed
bytes within the fat jar. This technique allows a bash script to be
embedded at the start of the JAR whilst still allowing `java -jar`
execution.

Fixes gh-1073
Improve error message on condition exceptions

Catch exceptions thrown from SpringBootCondition and re-throw with
more context.

See gh-1098