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

ui/build/ninja.go

@@ -59,6 +59,7 @@ func runNinja(ctx Context, config Config) {
 		"-w", "missingdepfile=err")
 
 	cmd := Command(ctx, config, "ninja", executable, args...)
+	cmd.Sandbox = ninjaSandbox
 	if config.HasKatiSuffix() {
 		cmd.Environment.AppendFromKati(config.KatiEnvFile())
 	}