rgw: build radosgw daemon as a shared lib + small executable
Majority of radosgw is contained in libradosgw.so. (/usr)/bin/radosgw
is now a few lines that calls radosgw_Main() in libradosgw.so.
The "zipper" work to modularize storage back-ends that will require
linking to the shared library to resolve the methods that they reference.
Putting the bulk of the implementation in a shared lib also allows for
unit testing to link with the shared lib for testing.
radosgw_Main() is the C++ implementation. For C linkage, radosgw_main()