os/KeyValueStore, MemStore: fix warning

os/MemStore.cc: In member function 'void MemStore::_do_transaction(ObjectStore::Transaction&)':
os/MemStore.cc:956:18: warning: unused variable 'expected_object_size' [-Wunused-variable]
os/MemStore.cc:957:18: warning: unused variable 'expected_write_size' [-Wunused-variable]
os/KeyValueStore.cc: In member function 'unsigned int KeyValueStore::_do_transaction(ObjectStore::Transaction&, KeyValueStore::BufferTransaction&, ThreadPool::TPHandle*)':
os/KeyValueStore.cc:1426:18: warning: unused variable 'expected_object_size' [-Wunused-variable]
os/KeyValueStore.cc:1427:18: warning: unused variable 'expected_write_size' [-Wunused-variable]

Signed-off-by: Sage Weil <sage@redhat.com>
Add random_cache.hpp to Makefile.am

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
(cherry picked from commit a3e5c6d632119febd2150944a6f2cbce33cfda3a)