Implement linux sandboxing with nsjail

This really only initializes the sandbox, it does not attempt to change
the view of the filesystem, nor does it turn off networking.

Bug: 122270019
Test: m
Test: trigger nsjail check failure; lunch; m; cat out/soong.log
Test: USE_GOMA=true m libc
Change-Id: Ib291072dcee8247c7a15f5b6831295ead6e4fc22