Remove ceilometer.conf.sample

The check-uptodate.sh was removed from the tox checks and therefore
ceilometer.conf.sample is not tested any more to be up to date. As this
sample configuration file changes independently from the project, this check
failed on the gate time to time, as this file  needed to be updated manually.
In order to avoid the need of this periodic manual process, the sample file
is removed from git in this patch and an alternate solution is added for
generating the file manually. Also a README file is added to the place of the
config sample to document this change.

Change-Id: I0bbec0e86f63e6fcd691d626473ed8498024f7ab
Merge "Remove ceilometer.conf.sample"