Auto-add in sbt-jdi-tools when using java8

[er1c]

Warning:

[warn] The sbt-debug-adapter cannot work because the JDI tools are not loaded.
[warn] 
[warn] Consider adding the sbt-jdi-tools plugin to your `./project/project/plugins.sbt` file:
[warn] addSbtPlugin("org.scala-debugger" % "sbt-jdi-tools" % "x.y.z")
[warn] 

Possible solution: https://github.com/ensime/scala-debugger/blob/f8e69614d71786605b4baa8c62f0968683936d22/project/plugins.sbt#L7-L16

Needs to be adapted/tested in the AutoPlugin probably. And version should be 1.1.1

[adpi2]

Another possible solution:

• Before running the debug server we check the java version
• If java version == 8 we find the tools.jar file and we create a new class loader with it
• We use this new class loader to load the debuggee runner classes and the DebugServer

The hard part is to create a correct class loader:

• tools.jar must be in a parent class loader of the scala-debug-adapter class loader
• no class loaded by this class loader should be accessible to the DebugAdapterPlugin directly to avoid linkage error.

All in all this solution seems a bit too convoluted. It will be hard to make it work and it will be hard to maintain.