hie.yaml discovery logic does not account for parent directories with no read permissions

[mbg]

I originally reported this issue as ghcide#314 but was advised there that the error probably originates in logic implemented by hie-bios instead.

The issue is that we are using ghcide on a shared system where users don't have read permissions for a parent directory of their home directories. This results in the following crash during step 3 of the startup of ghcide:

Step 3/6, Cradle 1/1: Implicit cradle for /[directory without read permissions]/[username]/[project]
ghcide: /[directory without read permissions]: getDirectoryContents:openDirStream: permission denied (Permission denied)

This happened with ghcide compiled using the current HEAD at the time (a0aa013) which appears to be using hie-bios-0.3.2.

A workaround is to have an explicit hie.yaml file in the current directory.