Replace Ceilometer ClientException with HTTPException

ClientException was removed from Ceilometer client. Replace it
with HTTPException.

Change-Id: I8707593861939b1218e42ff957171e97e225942f
Closes-bug: #1372416
(cherry picked from commit e36ff388c95927b53ba60d7a7f764d484ae9721d)
Merge branch 'stable/icehouse' of https://github.com/openstack/horizon into stable/icehouse