Embedded MongoDB is now auto-configured when it is on the classpath.
The Mongo instance will listen on the port specified by the
spring.data.mongodb.port property. If this property has a value of
zero and randomly allocated port will be used. In such an event, the
MongoClient created by MongoAutoConfiguration will be automatically
configured to use the port that was allocated.

By default, MongoDB 2.6.10 will be used. This can be configured using
the spring.embedded-mongodb.version property. Mongo's sync delay
feature is enabled by default. This can be configured using the
spring.embedded-mongobd.features property.

Closes gh-2002