Add connectorCapabilities global object

[duffn]

Purpose

This PR is to support the new connectorCapabilities object added to loopback-datasource-juggler as discussed here: loopbackio/loopback-datasource-juggler#1091.

This object will allow connectors to tell the tests in basic-querying.test.js whether or not they support a certain operator, so new operators added do not cause downstream connector tests to fail. Tests run when the operator is supported and do not run when it is not.

Example

In a connector's test/init.js

global.connectorCapabilities = {
  ilike: false,
  nilike: false,
};

In loopback-datasource-juggler test/basic-querying.test.js

var itWhenIlikeSupported = connectorCapabilities.ilike ? it : it.skip.bind(it);

itWhenIlikeSupported('should support "like" that is satisfied', function(done) {
  User.find({where: {name: {like: 'John'}}}, function(err, users) {
    if (err) return done(err);
    users.length.should.equal(1);
    users[0].name.should.equal('John Lennon');
    done();
  });
});

[slnode]

Can one of the admins verify this patch?

[slnode]

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

[slnode]

Can one of the admins verify this patch?