Sashi cli and rootless dockerd fixes (#122)

* Fixed sashi cli create json construction issue
* Properly applied rootless slirp4netns port driver.
* Added dockerd max-concurrent-downloads.
* Changed some debug logs to info.

src/util/util.cpp

@@ -451,7 +451,7 @@ namespace util
             {
                 if (output.back() == '\n')
                     output.pop_back();
-                LOG_DEBUG << output;
+                LOG_INFO << output;
             }
         }