Add support for changed rados_write API.

Seems from version 0.68 to 0.69 the rados_write
function all of a sudden gives back 0 when succeeded and
no longer the actual bytes it wrote. As we also want to
support the old API it now checks the LIBRADOS_VERSION_CODE

src/stored/backends/rados_device.c

@@ -160,7 +160,10 @@ ssize_t rados_device::d_read(int fd, void *buffer, size_t count)
 
 /*
  * Write data to a volume using librados.
+ *
+ * Seems the API changed everything earlier then 0.69 returns bytes written.
  */
+#if LIBRADOS_VERSION_CODE <= 17408
 ssize_t rados_device::d_write(int fd, const void *buffer, size_t count)
 {
    if (m_ctx) {
@@ -179,6 +182,26 @@ ssize_t rados_device::d_write(int fd, const void *buffer, size_t count)
       return -1;
    }
 }
+#else
+ssize_t rados_device::d_write(int fd, const void *buffer, size_t count)
+{
+   if (m_ctx) {
+      int status;
+
+      status = rados_write(m_ctx, getVolCatName(), (char *)buffer, count, m_offset);
+      if (status == 0) {
+         m_offset += count;
+         return count;
+      } else {
+         errno = -status;
+         return -1;
+      }
+   } else {
+      errno = EBADF;
+      return -1;
+   }
+}
+#endif
 
 int rados_device::d_close(int fd)
 {