Clarify logging in lockutils

The old logging statements in lockutils made for some confusing log
entries where it would appear a given lock was acquired multiple
times by different threads at the same time.  See referenced bug
for details.

In order to alleviate that confusion, this change does a few things:
1) Adds an explicit "acquired" message inside the lock so it is
   clear when the lock was actually acquired.
2) Moves the release message inside the semaphore so there's no
   chance of it being logged out of order.
3) Removes the "Got semaphore" message and splits it into two
   separate messages depending on whether the semaphore was found
   in the weakref dictionary.  Making it clear which code path
   was followed should help with future debugging.

This is the Nova port of oslo-incubator change
If863c9d3896bc786f3c9c46196ebb0766e57d863

Change-Id: I530befb42a963a40e7d5bf8d4d81fc097e1cb309
Partial-Bug: #1367941
Merge "Clarify logging in lockutils"