Warnings to be fixed - memory acess

[Jiri Srba]

When running on Mac with Java 9 I get the following warnings that should be fixed:

WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by dk.aau.cs.util.MemoryMonitor (file:/Users/srba/dev/tapaal-fix-1756865/release-version/) to field java.lang.ProcessImpl.pid
WARNING: Please consider reporting this to the maintainers of dk.aau.cs.util.MemoryMonitor
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

[Kenneth Yrke Jørgensen (yrke)]

It seems like this might be an unsupported hack: "For example on Macs, it returns java.lang.UnixProcess which has a private field called pid. Using Reflection you can easily get the value of this field. This is admittedly a hack, but it might help. What do you need the PID for anyway?" https://stackoverflow.com/questions/4750470/how-to-get-pid-of-process-ive-just-started-within-java-program/5578924

We need to find a supported way of getting the process PID, but until then I guess I would be safe to ignore the warning.

[Kenneth Yrke Jørgensen (yrke)]

Since Java 9 class Process has new method long pid(). However, this requires that we update the language version to 11, which should be ok, as 1.8 is soon EOL.

[Kenneth Yrke Jørgensen (yrke)]

Java version is updated to 11, so we replaced the existing implementation with net pid() method