Removed unnecessary inclusion of iostream

Removed unnecessary inclusion of iostream

In several files the iostream wasn't being used, so it got removed.
In other files the iostream inclusion was replaced by including iosfwd
(for forward declarations), which is much smaller header than iostream,
  so in theory should reduce compilation time.
To make this work some of the functions must have been moved from .h to .cc file.
3 functions also needed to have inline removed - this shouldn't affect
performance in any way: two of them are
probably too long to have been inlined anyway and the third one is for
error reporting, so probably won't be called too often.

test/Makefile-client.am: added linker libs

This was required to avoid linker error when linking
src/test/cls_rbd/test_cls_rbd.cc file. Makefile was specyfing
libcommon.a as a part of a linker command even though this wasn't
required and wasn't being linked against. When inline functions from
buffer.h were moved to buffer.cc(and inline was removed) the
libcommon.a library became necessary. This wouldn't link without also
including additional libraries(CRYPTO_LIBS and EXTRA_LIBS)

Signed-off-by: Michal Jarzabek <stiopa@gmail.com>