Sync models with migrations.

There are a lot of difference in models and actual db state
from migrations.
This patch fixes:
- wrong type of column,
- wrong length of column,
- missing indexes,
- extra indexes,
- errors.

bp: ceilometer-db-sync-models-with-migrations

Change-Id: I7f721ea604c0e1dfb8663c3acbaba66dc994e180
Rename get_counters to get_samples

Now counter has been renamed to sample, so it is better that
we update the function get_counters to get_samples.

Implements part of blueprint remove-counter

Change-Id: I908ea347f8d0fd4b5ef4b76eee6de98da5d2e0ca
Merge "Sync models with migrations."
Merge "Rename get_counters to get_samples"