asset precomiled test

So a little unsure about the proper way to not run on 5.2 but run against upstream and 5.3.  If you have any better ideas, enlighten me.  :)
If you're testing to see if a file/dir exists, I recommend using test:
`test -d /var/www/miq/vmdb/public/assets`

To keep things sane, explicitly using /usr/bin/test to avoid the shell builtin is probably a wise move.