Add Statistics Collection loop

This patch adds a new service which provides
an endless loop to update statistics information.
There is no actual code for stats themselves.

the intension is to save a collected stats to DB
on a periodic basis.

Change-Id: Ia00a5068c2f744b0318a523860ccc5eba225868e
Partly-Implements: blueprint api-request-stats
Add per API call statistics

This patch adds a new decorator which calls a stats
collection code to collect usage information per tenant

StatisticsCollection class is added a a stats storage.

Add hostname to stats

As Murano has multi-service deployment it is
necessary to add hostname to each stats
in order to understand which API service
provides them.

Add DB model for stats

This patch adds a new DB model to keep API stats in the DB.
As it is possible to have multiple Murano API servers
we will keep stats for each Murano API instance

Fix stats update to save data to DB

Fixed issues with column names
Added logic to calculate request\sec
and errors\sec based on previous values

Change-Id: Id5c3cdc90700563aff881e5831285a1330a2c034
Partly-Implements: blueprint api-request-stats
Merge "Add Statistics Collection loop"
Merge "Add per API call statistics"