test: bump loopback-datasource-juggler version

The .ping support added in 2ffa87a and the .ping() support tests added
in 8d86533 require loopback-datasource-juggler@2.6.0.

Expanded tests in test/default-scope.test.js added in afbfc75 require
loopback-datasource-juggler@2.10.0.
test: Use mongodb on localhost under CI

Override default (which is loopbackrc) to use mongodb instance on
localhost when running under CI (Jenkins or Travis).
Merge pull request #62 from fix/upgrade-loopback-datasource-juggler