Since commit 8f40b6a61985dee97c2006b747fbc5227819cf01, specifying a custom kernel or boot file in config.json no longer works, because these file paths are overwritten with the paths from the current Nanos release.
This commit fixes the above issue so that file paths specified in config.json are only overwritten if a Nanos version (or a nightly build) is specified by the user.
Since commit 8f40b6a61985dee97c2006b747fbc5227819cf01, specifying a custom kernel or boot file in config.json no longer works, because these file paths are overwritten with the paths from the current Nanos release. This commit fixes the above issue so that file paths specified in config.json are only overwritten if a Nanos version (or a nightly build) is specified by the user.