Refactor work with TaskLog in sqlalchemy.api

Add _task_log_get_query() private method
It is used to remove from task_log_get() and task_log_get_all() session.
parametr and save performance.

task_log_get() method
Remove session parameter from public method.

task_log_get_all() method
Remove session parameter from public method.

task_log_begin_task()
Remove session parameter from public method.
Remove unused return value.

task_log_end_task()
Remove session parameter from public method.
Use 1 db request instead of 2.
Remove unused return value.

blueprint db-session-cleanup

Change-Id: I2c8252de7978e8fddd800e903f18a73ee9a95034
Merge "Refactor work with TaskLog in sqlalchemy.api"
Merge remote-tracking branch 'citrix/master' into build-temp