crates/accounts: fix conflicting lock orders

[BurtonQin]

unlocked_secrets and unlocked are parking_lot::RwLock.
In fn sign(), unlocked_secrets.read() -> password() -> unlocked.write().

openethereum/crates/accounts/src/lib.rs

Lines 449 to 455 in 6a42062

	let account = self.sstore.account_ref(&address)?;
	match self.unlocked_secrets.read().get(&account) {
	Some(secret) => Ok(self.sstore.sign_with_secret(&secret, &message)?),
	None => {
	let password = password
	.map(Ok)
	.unwrap_or_else(|| self.password(&account))?;

openethereum/crates/accounts/src/lib.rs

Lines 372 to 373 in 6a42062

	fn password(&self, account: &StoreAccountRef) -> Result<Password, SignError> {
	let mut unlocked = self.unlocked.write();

There are two other cases where unlocked is locked before unlocked_secrets.
If they are concurrent with the above case, a deadlock may happen.

1. openethereum/crates/accounts/src/lib.rs

   Lines 420 to 422 in 6a42062

   	pub fn is_unlocked(&self, address: &Address) -> bool {
   	let unlocked = self.unlocked.read();
   	let unlocked_secrets = self.unlocked_secrets.read();

2. openethereum/crates/accounts/src/lib.rs

   Lines 343 to 354 in 6a42062

   	let mut unlocked = self.unlocked.write();
   	if let Some(data) = unlocked.get(&account) {
   	if let Unlock::Perm = data.unlock {
   	return Ok(());
   	}
   	}
   	if self.unlock_keep_secret && unlock == Unlock::Perm {
   	// verify password and get the secret
   	let secret = self.sstore.raw_secret(&account, &password)?;
   	self.unlocked_secrets
   	.write()

The fix is to assign unlocked_secrets.read() to a variable secrets and explicitly drop it before calling password().