Description of problem:

unable to unset the "CDN SSL version" settings from the UI of Satellite

Version-Release number of selected component (if applicable):
satellite-6.11

How reproducible:


Steps to Reproduce:
1. Visit to WebUI --> admin --> settings --> content --> CDN SSL version
2. Change the value from the drop-down  SSLv23 and TLSv1
3. Now if you do not need any of these values, you can not change it to Default "Empty"

Actual results:

We can not unset the value to set the Empty value in the BOX 

Expected results:

Need an option to unset the value 


Additional info:

# hammer settings info --name cdn_ssl_version
Id:            cdn_ssl_version
Name:          cdn_ssl_version
Description:   SSL version used to communicate with the CDN
Category:      Content
Settings type: 
Value:         TLSv1


To unset the value : 

# hammer settings set --name cdn_ssl_version --value=''