Provide service type management code structure

Reasons for refactoring:
- current code structure is orientied on mysql management implementation;
- there is no chanse to make new service types management
code fittable in current package/module structure;
- backuping process implementation is mysql/percona-orientied,
it should be renamed and should be configurable due to service type;
- "query" is abstract word for querying into database,
current query.py implementation is SQL orientied - it should be renamed;

Updates:
1.Providing new package hierarchy:
   guestagent/manager/service_type/service.py
   guestagent/manager/service_type/manager.py
   guestagent/manager/service_type/system.py
2.Renaming strategy implementations per each service_type
   guestagent/strategies/backup/mysql_impl.py
3.Externalizing operating system definer form system.py
 which used in pkg.py
4.Renaming query to sql_query.

Implement: blueprint refactor-ga-for-other-engines-support
Change-Id: I5fa5f037056bedf5464e99720cbe03b877c27fba
Merge "Provide service type management code structure"