hst/container: optional runtime and tmpdir sharing

Sharing and persisting these directories do not always make sense. Make it optional here.

Closes #16.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/hpkg/app.go

@@ -130,6 +130,7 @@ func (app *appInfo) toHst(pathSet *appPathSet, pathname *check.Absolute, argv []
 	if app.Multiarch {
 		config.Container.Flags |= hst.FMultiarch
 	}
+	config.Container.Flags |= hst.FShareRuntime | hst.FShareTmpdir
 	return config
 }