Provide better error message when inspec.yml is invalid

[adamleff]

Currently, if the inspec.yml for a profile is invalid (such as including
an improperly-defined multi-line string), InSpec will throw an exception
from the YAML parser that does not given a clear indication that the
issue was encountered while parsing the inspec.yml file.

This change introduces a better exception message to clue the user into
where the problem actually lies.

Fixes #1549.

[chris-rock]

@adamleff Awesome. That is so helpful for users.

$ inspec exec examples/profile
Unable to parse inspec.yml: line 8, could not find expected ':' while scanning a simple key

I was playing with the idea for InSpec check:

$ inspec check examples/profile
/Users/chartmann/Development/compliance/inspec/lib/source_readers/inspec.rb:47:in `rescue in load_metadata': Unable to parse inspec.yml: line 8, could not find expected ':' while scanning a simple key (RuntimeError)
	from /Users/chartmann/Development/compliance/inspec/lib/source_readers/inspec.rb:42:in `load_metadata'
	from /Users/chartmann/Development/compliance/inspec/lib/source_readers/inspec.rb:34:in `initialize'
	from /Users/chartmann/Development/compliance/inspec/lib/source_readers/inspec.rb:14:in `new'
	from /Users/chartmann/Development/compliance/inspec/lib/source_readers/inspec.rb:14:in `resolve'
	from /Users/chartmann/Development/compliance/inspec/lib/utils/plugin_registry.rb:18:in `block in resolve'
	from /Users/chartmann/Development/compliance/inspec/lib/utils/plugin_registry.rb:17:in `each'
	from /Users/chartmann/Development/compliance/inspec/lib/utils/plugin_registry.rb:17:in `resolve'
	from /Users/chartmann/Development/compliance/inspec/lib/inspec/source_reader.rb:14:in `resolve'
	from /Users/chartmann/Development/compliance/inspec/lib/inspec/profile.rb:58:in `for_path'
	from /Users/chartmann/Development/compliance/inspec/lib/inspec/profile.rb:69:in `for_fetcher'
	from /Users/chartmann/Development/compliance/inspec/lib/inspec/profile.rb:75:in `for_target'
	from /Users/chartmann/Development/compliance/inspec/lib/inspec/cli.rb:67:in `check'
	from /Users/chartmann/.rvm/gems/ruby-2.3.3/gems/thor-0.19.4/lib/thor/command.rb:27:in `run'
	from /Users/chartmann/.rvm/gems/ruby-2.3.3/gems/thor-0.19.4/lib/thor/invocation.rb:126:in `invoke_command'
	from /Users/chartmann/.rvm/gems/ruby-2.3.3/gems/thor-0.19.4/lib/thor.rb:369:in `dispatch'
	from /Users/chartmann/.rvm/gems/ruby-2.3.3/gems/thor-0.19.4/lib/thor/base.rb:444:in `start'
	from /Users/chartmann/Development/compliance/inspec/bin/inspec:12:in `<top (required)>'
	from /Users/chartmann/.rvm/gems/ruby-2.3.3/bin/inspec:22:in `load'
	from /Users/chartmann/.rvm/gems/ruby-2.3.3/bin/inspec:22:in `<main>'
	from /Users/chartmann/.rvm/gems/ruby-2.3.3/bin/ruby_executable_hooks:15:in `eval'
	from /Users/chartmann/.rvm/gems/ruby-2.3.3/bin/ruby_executable_hooks:15:in `<main>'

Instead of showing a parse error, we should return a response with the error that the yml is not correct. What do you think. Should we do that in another PR?

[adamleff]

@chris-rock If you're talking about changing the output of inspec check to simply a be a one-line message indicating the error and eliminate the stacktrace, I'm totally good with that too and happy to do that in this PR.

If not though, can you restate your suggestion because I'm possibly not understanding it :)

[chris-rock]

As discussed offline, we will do inspec check as a separate ticket.

[chris-rock]

It is so great to make the UX better @adamleff Thank you @graham1228 for reporting that issue.