Error: Cannot retrieve repository metadata (repomd.xml) for repository: sandbox. Please verify its path and try again 2018-02-01 10:28:37,458 - Failed to install package mongodb-org-shell. Executing '/usr/bin/yum clean metadata'
MongoDB is not within the hadoop stack, so it will not be possible to install it via Ambari out of the box. I would also go the way via direct install on the shell, as @Gourav Gupta suggests, but as the Sandbox is not based on Ubuntu or Debian, you will need to follow the instruction to install it on Centos: