Remove redundant meter (name,type,unit) tuples from Resource model

Fixes bug 1267162

Previously, a list of meter (name,type,unit) tuples with per-sample
cardinality was added to the Resource model by the storage driver
get_resource method.

However this potentially huge and highly repetitive list was then
promptly discarded by the API layer, as the meter links in the API
Resource representation are populated via subsequent calls into
the storage driver get_meters method.

Now, we avoid the scaling issue by suppressing the creation of
this unused meter list.

Change-Id: I18dee7552836c724798ea1340e2e933c09d8a294
(cherry picked from commit 7c4c0e8fc098fbadec2e30ea2bdf1068b5b4288a)