Adding comparison operators in query for event traits

In EventFilter we have an optional parameter 'op' in traits_filter part. But up
to date usage of this param has been implemented only in Hbase and
Mongodb backends. However in API we can use only 'op'='eq'.

This change improves usage of parameter 'op' in query for events in api, and
adds possibility to use comparison in query with SQL backend.

Some tests are also added to cover using of this new feature.

Closes-bug: #1354009
Change-Id: I4824800eac7270bcfa10882a735e48d80bf32712
Merge "Adding comparison operators in query for event traits"