Error logging can be improved when the DB write is not possible

[raokrutarth]

The code block below creates a new dict but fails when the file system does not allow file locks (or something else related to permissions).

def _get_queue_mapper_db_sesh() -> persistqueue.PDict:
    db_path = environ.get("GENERIC_EVENT_DB_PATH")
    assert db_path is not None, f"Invalid queue mapping db path: {db_path}"
    return persistqueue.PDict(
        path=db_path,
        name="generic_proxy_queues_mapppings",
        multithreading=True,
    )

But, the error points to a missing attribute at first instead of terminating the app at the DB lock error:

# Traceback (most recent call last):
#   File "<string>", line 17, in <module>
#   File "<string>", line 10, in _get_queue_mapper_db_sesh
#   File "/opt/python/3.8.5/lib/python3.8/site-packages/persistqueue/pdict.py", line 22, in __init__
#     super(PDict, self).__init__(path, name=name,
#   File "/opt/python/3.8.5/lib/python3.8/site-packages/persistqueue/sqlbase.py", line 89, in __init__
#     self._init()
#   File "/opt/python/3.8.5/lib/python3.8/site-packages/persistqueue/sqlbase.py", line 101, in _init
#     self._conn = self._new_db_connection(
#   File "/opt/python/3.8.5/lib/python3.8/site-packages/persistqueue/sqlbase.py", line 129, in _new_db_connection
#     conn.execute('PRAGMA journal_mode=WAL;')
# sqlite3.OperationalError: database is locked
# Exception ignored in: <function SQLiteBase.__del__ at 0x7fb9913efaf0>
# Traceback (most recent call last):
#   File "/opt/python/3.8.5/lib/python3.8/site-packages/persistqueue/sqlbase.py", line 202, in __del__
#     self._getter.close()
# AttributeError: 'PDict' object has no attribute '_getter'