Use /dev/zero for disk rate check

/dev/random is slow by design and probably a bottleneck in the check. /dev/zero should be faster.

host/examples/rx_samples_to_file.cpp

@@ -64,7 +64,7 @@ double disk_rate_check(const size_t sample_type_size,
         boost::filesystem::path(file).parent_path() / boost::filesystem::unique_path();
 
     std::string disk_check_proc_str =
-        "dd if=/dev/random of=" + temp_file.native()
+        "dd if=/dev/zero of=" + temp_file.native()
         + " bs=" + std::to_string(samps_per_buff * channel_count * sample_type_size)
         + " count=100";