CXX-270 change mongoclient target to driver, add examples to test target

includes refinements discussed in #145 
Interesting that the alias doesn't also encompass the mongoClientSharedLib. It should. Also, the variable to which it is assigned, 'buildMongClientAlias' appears to be unused. Can you do the following:

- Remove the variable assignment
- After line 379, can you add

libEnv.Alias('driver', mongoClientSharedLib)