Ref https://www.sqlite.org/c3ref/initialize.html:
The sqlite3_initialize() interface is threadsafe, but
sqlite3_shutdown() is not.
We currently call `sqlite3_shutdown` from all threads as part of
`sqlite_init_multithreaded`, and this has been observed to have
adversarial effects during startup if many threads receive their first
inbound request at the same time. The apparent motivation behind
calling shutdown is to make the subsequent calls to `sqlite3_config`
succeed, since these ordinarily return SQLITE_MISUSE if called
multiple times. However, this function is also documented to not be
thread safe, so introduce a barrier that ensures we only initialize
once over all threads.
Because:
1. According to sqlite3 docs sqlite3_initialize() and sqlite3_shutdown() are not must to be invoked
2. sqlite3_initialize() is never called explicilty
3. sqlite3_shutdown() is not threadsafe and sqlite_init_multithreaded is not called holding a lock
4. According to docs all connections must be closed before invoking sqlite3_shutdown() but they are not (from the different threads).
Possible issue:
sqlite3_config must be called before sqlite3_initialize() or after sqlite3_shutdown() (and only once?)
Coturn does not disconnect database properly when shutdown.
This behavior causes accumulation of sockets for database with TIME_WAIT.
Especially, `turnadmin` is recommended to manage userdb,
but use of `turnadmin` from other application or scripts
can run out of socket resource due to above problem.
This patch adds database disconnection when shutdown
for both of `turnserver` and `turnadmin`.
Fixes#366
