Fix metering service endpoint path

After installing ceilometer with the metering cookbook, invoking the
ceilometer CLI fails because the API base URL used is
http://127.0.0.1:8777/v1/v2 which means that the base endpoint path of
/v1 is incorrect and it should be simply /.

Change-Id: Id65a17a888175c7b2fe2d3171147cedb66921cc9
Partial-Bug: #1277742
allow overriding all endpoint hosts with a single attribute

similar to the pattern in the messaging and database attributes, this is
a convenience change that allows you to set all endpoint host values to
something other than the default of 127.0.0.1, by only overriding a
single attribute in your environment.

Quite often one will want to set all endpoints to the same IP, for
example in the case where you are deploying a 'controller' node, and at
the moment every endpoint host attribute has to be overridden
individually.

All endpoint host attributes can still be overridden individually if
desired.

Change-Id: I7dd96f69c3eaa9156513663f08dafbddf1c1ffd8
Merge "Fix metering service endpoint path"
Merge "allow overriding all endpoint hosts with a single attribute"