OSD: use !empty() instead of size() > 0

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
ReplicatedPG: prefer prefix ++operator for non-trivial iterator

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
RGWObjManifest: prefer prefix ++/--operator for non-trivial iterator

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
ceph_erasure_code.cc: prefer prefix ++operator for non-trivial iterator

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
ErasureCodeBench: prefer prefix ++operator for non-trivial iterator

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
TestRados.cc: use !empty() instead of size()

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
BackedUpObject::get_xattr()  pass function parameter by reference

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>