Add Connection and Endpoint structs which wrap the various connection
parameters. Additionally, on construction performs simple read/write
test.
Add PhysicalBuffer class to conveniently wrap RMA2_Region.
Add helper function throw_on_error to handle exceptions while
establishing and testing the connection.
Add definitions of exceptions to throw.

Change-Id: Ie4d9315208778ec7c484ce3c023775e1eb1c78d1