Implements monitoring-network

This feature collects the network information(devices, connect statuses
and statistices) via North Bound API from the SDN controller.

Implements: blueprint monitoring-network

Change-Id: Ifaa88fd3135dafe8ae3e83e03b76fb9b7e1b0904
rename meter table to sample

as we branch common meter definition data to it's own table,
we rename table containing raw data to more appropriate name:
sample

blueprint: meter-table-sql
Change-Id: I55c86540098225a3d52116df8b27854483921ee9
sample table contains redundant/duplicate data

create a meter table to store meter definition attributes:
- name
- type
- unit

blueprint: meter-table-sql
Closes-Bug: #1211985
Change-Id: I4dd510e66d64226b03cfce8d7dd5e77937793ba3
Remove code duplication

Remove code duplication from impl_mongodb and impl_db2 as both of
these drivers use pymongo. This is a multiple step process as there
are several differences between the implementation of these drivers.

The first step is about to move the identical functions to a common
base file, called pymongo_base with a Connection class, from which
the Connection class of both drivers will be inherited.

Change-Id: Ib3c250213cda5450c96c6e495f56623ed7ac0490
Fix the way how metadata is stored in HBase

The goal of this patch is to fix filtering on metadata.
In HBase we should use the same approach as in SQL now:
store raw metadata as well as flattened one.
When user sends get request on meters, samples or resources
it is possible not to fetch all the data but construct corresponding
filter based on flattened metadata values.
Unfortunatelly, it is not possible not to store raw metadata because
flattening on API level is done in a different way. This
improvement is postponed till API v3.

Change-Id: I1206535ab12037817175d5e79716b223594f246a
Merge "Implements monitoring-network"
Merge "rename meter table to sample"
Merge "sample table contains redundant/duplicate data"
api: export recorded_at in returned samples

Change-Id: I970bc82d70fd75cbb25ea6c7e0778521aaa9b255
Blueprint: storage-sample-timestamp
Merge "Fix the way how metadata is stored in HBase"