Fixes datasource generation with community connector

[amuramoto]

Community connectors are not listed in availableConnectors, causing the following when a user chooses 'other' and enters a community connector:

ERROR Cannot read property 'package' of undefined

Fix makes function return when this is the case, allowing generator to proceed creating skeleton record in datasources.json

[slnode]

Can one of the admins verify this patch? To accept patch and trigger a build add comment ".ok\W+to\W+test."

[superkhau]

@amuramoto Your PR is failing on Travis, can you check it out?

[amuramoto]

@superkhau Tests appear to be failing due to PR #173 which is still under review

[superkhau]

@amuramoto Cool, I'll leave this one for @bajtos to review as he is more familiar with this module. It LGTM, but can't really tell with Travis not passing.

[superkhau]

@amuramoto Can you add a unit test to verify your changes?

[bajtos]

When we don't have any information about the custom connector selected for a new datasource, then I think we should assume the package name is same as the connector name and run npm install {this.connector}.

@amuramoto @superkhau @ritch @raymondfeng Thoughts?

[bajtos]

@amuramoto thank you for the pull request, this is indeed a bug that needs to be fixed!

I left a comment above, I think we should take a different approach. Also please add a unit-test to verify your change and prevent regressions in the future, see these two existing tests for inspiration:

generator-loopback/test/datasource.test.js

Lines 45 to 81 in 8fbdb0d

	it('allow connector without settings', function(done) {
	var modelGen = givenDataSourceGenerator();
	helpers.mockPrompt(modelGen, {
	name: 'kafka1',
	customConnector: '', // temporary workaround for
	// https://github.com/yeoman/generator/issues/600
	connector: 'kafka',
	installConnector: false
	});
	var builtinSources = Object.keys(readDataSourcesJsonSync('server'));
	modelGen.run(function() {
	var newSources = Object.keys(readDataSourcesJsonSync('server'));
	var expectedSources = builtinSources.concat(['kafka1']);
	expect(newSources).to.have.members(expectedSources);
	done();
	});
	});
	it('should install connector module on demand', function(done) {
	var modelGen = givenDataSourceGenerator();
	helpers.mockPrompt(modelGen, {
	name: 'rest0',
	customConnector: '', // temporary workaround for
	// https://github.com/yeoman/generator/issues/600
	connector: 'rest'
	});
	modelGen.run(function() {
	var pkg = fs.readFileSync(
	path.join(SANDBOX, 'package.json'), 'UTF-8');
	pkg = JSON.parse(pkg);
	/* jshint -W030 */
	expect(pkg.dependencies['loopback-connector-rest']).to.exist;
	done();
	});
	});

For posterity, the failing CI build is not waiting for #173, but for fixing our dependencies, per
#173 (comment)

Yeoman's latest release has a breaking change in prompts. We probably have to update our code.
yeoman/generator#926 The latest version of yeoman-environment 1.6.1 is breaking the unit test. The promptModule is causing problems.

[bajtos]

Closing in favour of #199