* SOLR-13984: add (experimental, disabled by default) security manager support.
User can set SOLR_SECURITY_MANAGER_ENABLED=true to enable security manager at runtime.
The current policy file used by tests is moved to solr/server
Additional permissions are granted for the filesystem locations set by bin/solr, and networking everywhere is enabled.
This takes advantage of the fact that permission entries are ignored if properties are not defined:
https://docs.oracle.com/javase/7/docs/technotes/guides/security/PolicyFiles.html#PropertyExp
Robert Muir