Cleanup/reduce redundancy between the test modules

Define the test sysctl node once in test_sysctl.ko, add glue Makefiles,
and remove unnecessary load/unload event handlers

Sponsored-by: EMC / Isilon Storage Division
Implement dummy module no-op handler to workaround caveat
discovered in PR # 192257

Sponsored-by: EMC / Isilon Storage Division
Move memguard/ and tools/ to freebsd/

Sponsored-by: EMC / Isilon Storage Division
Merge branch 'master' of https://github.com/yaneurabeya/scratch