core: compile as C++

Multi-step patch that will move code over to use the C++ RADOS API. This
is needed so we can access bufferlists, and avoid some weird parts of
the C API. For example, rados_exec takes a fixed size output buffer,
but it is difficult to predict the output size.

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
travis: add notification settings

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
core: convert code to use Rados C++ API

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
style: switch to 2 space indent for C++

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>