Report failed target but don't bail on whole manifest

[jsumners-nr]

See the discussion in #36 (review)

Currently, we will bail on a versioned test manifest completely if any target in that manifest fails for some reason. Known reasons are 1. target is defined but there is not a correlating dependency in the tests and 2. same as 1, but the minSupported attribute has been omitted. In other words, both of these are valid and should pass:

{
	targets: [{
		name: 'foo', minAgentVersion: '1.2.3'
	}],

	tests: [{
		dependencies: { 'foo': '>=1.0.0' },
		files: [ 'whatever.test.js' ]
	}]
}

{
	targets: [{
		name: 'foo', minSupported: '1.0.0', minAgentVersion: '1.2.3'
	}],

	tests: [{
		files: [ 'whatever.test.js' ]
	}]
}

We need to construct a test case that fails, and then refactor the implementation to only report the error for the offending target but continue with other targets in the manifest.