Java pipeline add posibility to share meven repository between docker images

[david-jezek]

Each run of new docker instance of java pipeline image create new own maven repository (.m2), which cause long startup time and long console output, which is unclear.
Use docker mount point to add shared disk space to speed up maven builds and get shorter output logs. There is possible risk to get local m2 repo to unclear state. So add possibility for teacher to clear (erase/delete) all files in maven local shared repository.