provide a clean way for management and driver-mapping customizations

* custom launchers can customize launch and management
* new driver-naming strategies can be defined and added
fix warning when deleting files
support config key for osgi cache dir, which now defaults to under mgmt base dir

running in /tmp is not recommended. we attempt as best we can to delete it if it looks transient,
but on `kill -9` there may be junk leftover under osgi/cache/
clean up ServerResource export persistence folder

previously made lots of messy web-persistence-XXX folders under ~/.brooklyn;
now there is a single `tmp` in there
This closes #340