Allow db instance conditional logging

Reason:
- config.template misses logging section;
- non-optional mysql logging is a performance killer (according to docs)

Changes:
- conditional logging via rendering config.template;
- tests.

Partionaly implements: blueprint dbinstance-log

Change-Id: I0ad7def9ec041c4a83a89558b7b3db389e03623a
Allow log files audit

Reason:
- audit process is required for database management

Changes:
- adding functionality for instance database log managements
dblog-create, dblog-list, dblog-show;
- tests.

Change-Id: I1485f172f55e98991537f835e3495f93bf91b11c
Implements: blueprint dbinstance-log