Modify SQLA session due to dispose of eventlet

Change openstack/common/db/sqlalchemy/session.py due
to use time.sleep() instead of eventlet.greenthread.sleep().
Function _greenthread_yield() renamed to _thread_yield().

Change-Id: I98987dc045ee5518ce0705213c5cec9b3aba8021
Modify lockutils.py due to dispose of eventlet

Change lockutils.py due to use threading.Semaphore instead of
eventlet.semaphore.Semaphore. Tests modified properly.

Change-Id: Ic3c5934577aff856ec71ba7e44b54aa963fda69c
Merge "Modify SQLA session due to dispose of eventlet"
Merge "Modify lockutils.py due to dispose of eventlet"