Fixed concurrent PUT requests to accounts or containers

When concurrent PUT requests come in for an account or container, the
resulting DB access will try to lock the DB for writing. Normal access
will retry when it encounters a locked DB, change 0fdad0d9 introduced
a cursor for doing the initialization which did not have the retry
capability, resulting in a hard failure.

Fixes bug 1243973

Change-Id: I73b219e0f5eacf314d87b4d5e56c03daf51b2eca
Fix DB locked error on commit

This bug was introduced in ef7f9e27; while moving timeout for execute
to the cursor wrapper, commit was moved as well; however commit is
purely a connection method, only execute is passed on to a cursor.
Added unit tests to check both methods for correct timeouts.

This manifested in a test failure as:
ERROR __call__ error with POST /sdb1/418/AUTH_d1c4b610b16a48de83219c696261009c/TestContainer-tempest-1572414684 :
Traceback (most recent call last):
  File "/opt/stack/new/swift/swift/container/server.py", line 486, in __call__
    res = method(req)
  File "/opt/stack/new/swift/swift/common/utils.py", line 1915, in wrapped
    return func(*a, **kw)
  File "/opt/stack/new/swift/swift/common/utils.py", line 687, in _timing_stats
    resp = func(ctrl, *args, **kwargs)
  File "/opt/stack/new/swift/swift/container/server.py", line 464, in POST
    broker.update_metadata(metadata)
  File "/opt/stack/new/swift/swift/common/db.py", line 677, in update_metadata
    conn.commit()
OperationalError: database is locked (txn: tx5065394f288740e69fcec-00528e184e)

Change-Id: I269b133fac53d4792d21b62f801cc0c0ccf337ea
Use upstream patched Pool.get

This works around an eventlet bug in eventlet 0.9.16.
This version properly keeps track of pool size accounting, and
therefore doesn't let the pool grow without bound. This patched
version is the result of commit
f5e5b2bda7b442f0262ee1084deefcc5a1cc0694 in eventlet and is
documented at https://bitbucket.org/eventlet/eventlet/issue/91

This patch includes full test coverage of the back-ported code, even
when the actually-installed eventlet is newer.

This fixes bug #1254119

Change-Id: I075bb5e40e08571d52fe17fcc3fa0e25be5befed