Misconfigured publish dir is not correctly detected

[ascorbic]

We try to fail the build when the root dir is set as the publish dir. However according to BugSnag quite a few seem to be slipping through, and it means the builds fail with a plugin error when it gets to the point of saving the cache. We should ensure that we are properly normalizing the paths, and ideally use the same check as the cache util uses.

[nickytonline]

@ascorbic, is this still an issue?

[ericapisani]

Closing due to inactivity