LOG4PHP-207: Using class MongoClient instead of Mongo

 - additional connection options support
 - support for replica tests
 - support for multiple hosts via connection string

Signed-off-by: Vladimir Gorej <gorej@codescale.net>
Signed-off-by: Ivan Habunek <ivan.habunek@gmail.com>
Minor fix for MongoDB tests

Made tearDown() check for the mongodb extension as well as setUp()
otherwise the tests would fail if extension was not loaded, instead
of being skipped.

Signed-off-by: Ivan Habunek <ivan.habunek@gmail.com>