What igor provided is good for a filter but I believe you were looking for a report. I'm not aware of any built-in report but here is a simple report that shows each managed machine and whether it is using HTTPS mode. It also shows the last time it succesfully used CEM which may be useful as you roll that out.
select vc.Name, vc.[IP Address], vc.[Domain]
,nz.InternetModeSupported,nz.IsOnInternet, nz.httpsmode
,cem.gateway, cem.[Last Success], cem.[Current]
from vComputer vc
left join Inv_AeX_AC_InternetGatewayDetails cem on cem._ResourceGuid = vc.Guid
left join Inv_AeX_AC_Network_Zone nz ON nz._ResourceGuid = vc.[Guid]
where vc.isManaged = 1
Also, it is not necessary to turn off HTTP. We are running an enviornment with HTTP and HTTPS enabled and CEM is working great.