validate: modify the validation of mounts.type
I‘m not familiar with solaris system, so I'm not sure if this is a right validation. But from here, It seems vfstab stores default mounted file systems not all supported file systems. Any comments from @opencontainers/runtime-tools-maintainers ?
Why is this in v0.7.0? I don't see anything about “solve options conflict problem” here (I'd expect v0.7.0 to only contain #414, but it currently doesn't). This looks like part of implementing config validation, so it belonged in v0.2.0. And with v0.2.0 cut, it should fall back to v0.3.0.
It's a validation about solaris but we are not familiar with it, at least I@liangchenye and I. We can't make sure whether it's right or not just from solaris's reference document. And I think we should perfect Linux related validations first. Other platform's may be later. So, moving it to v0.7, just want to put it into low priority. If anyone's familiar with solaris, you can review this PR. Though it's in v0.7, we can merge this before v0.7.