A more verbose error message for schema validation

[jugonzal07]

Hi all,

I found myself a bit stumped debugging upgrading to a new version of copper in a new environment only to find that I was taking this message too literally.

copper/copper/cli.py

Lines 27 to 33 in fe18acd

	try:
	f = json.load(input_file)
	# Validate input file
	assert copper.Schema(f).validate() == True
	except:
	raise ValueError("Could not read the input file. A JSON file is expected.")

While I was able to piece together it was due to not having a valid schema, I thought the error was reporting that my JSON file was in the wrong place. Perhaps different error messages for finding the file and another for schema validation would be more clear!

[lymereJ]

That makes sense, thanks for suggesting it. I'll work something out soon!