MD5 Calculation on blob_get_blob should use native code thread and not node js crypto library

[jeniawhite]

Environment info

• Version: VERSION
• Deployment: AZURE | AWS | GCLOUD | ESX | VBOX | DEV
• Customer: NAME

Actual behavior

1. In blob_get_blob we calculate the md5 using the crypto library in our node js process (single thread)

Expected behavior

1. We should move the calculation to the native c++ thread that will calculate the md5

Steps to reproduce

Screenshots or Logs or other output that would be helpful