Hard-to-understand error message when building from a dir missing porter.yaml

[edespong]

Describe the bug

When manually creating a porter.yaml and trying to build it, I mistakenly named it porter.yml. Then when running porter build it fails and the error message could be more clear to help indicating the error. Other, commands like porter publish are a lot more helpful when doing something wrong.

To Reproduce

> mkdir unclear-message
> cd unclear-message
> porter create
> mv porter.yaml porter.yml
> porter build

Expected behavior

An output more in line with what porter publish gives:

$ porter publish
could not find porter.yaml in the current directory ~/unclear-message, make sure you are in the right directory or specify the porter manifest with --file

Porter Command and Output

$ porter build
unable to read manifest file : could not read the manifest at "": read ~/unclear-message: is a directory
unable to generate manifest: unable to read manifest file : could not read the manifest at "": read ~/unclear-message: is a directory

Version

porter v1.0.14 (0e739d8)