Allow query logging

Reason: Each query which is executed through sqlalchemy are logged,
because engine had been initialized with parameter echo=True,
this flag cause security issue - logging insecure user credentials.

Changes:
- adding flag to guest config which allows to
unable/disable insecure/secure query logging,
default value for insecure logging - False;
- engine init parameter echo depends on config value

Closes-Bug: #1224700
Change-Id: I2e0e5970a981f16ce1abe96f012ed7618f57287a
Merge "Allow query logging"