Replace dev chain special case with preset

Add --min-gas-price (does the same as legacy --gasprice) and tweak
gas_pricer_config() and test cases.  Dev preset will still be
overridden by CLI arguments, including --gasprice.

parity/cli/config.full.toml

@@ -101,6 +101,7 @@ reseal_min_period = 4000
 reseal_max_period = 60000
 work_queue_size = 20
 relay_set = "cheap"
+min_gas_price = ""
 usd_per_tx = "0.0025"
 usd_per_eth = "auto"
 price_update_period = "hourly"

parity/cli/mod.rs

@@ -269,6 +269,8 @@ usage! {
 			or |c: &Config| otry!(c.mining).tx_time_limit.clone().map(Some),
 		flag_relay_set: String = "cheap",
 			or |c: &Config| otry!(c.mining).relay_set.clone(),
+		flag_min_gas_price: Option<String> = None,
+			or |c: &Config| otry!(c.mining).min_gas_price.clone().map(Some),
 		flag_usd_per_tx: String = "0.0025",
 			or |c: &Config| otry!(c.mining).usd_per_tx.clone(),
 		flag_usd_per_eth: String = "auto",
@@ -542,6 +544,7 @@ struct Mining {
 	tx_gas_limit: Option<String>,
 	tx_time_limit: Option<u64>,
 	relay_set: Option<String>,
+	min_gas_price: Option<String>,
 	usd_per_tx: Option<String>,
 	usd_per_eth: Option<String>,
 	price_update_period: Option<String>,
@@ -808,6 +811,7 @@ mod tests {
 			flag_tx_gas_limit: Some("6283184".into()),
 			flag_tx_time_limit: Some(100u64),
 			flag_relay_set: "cheap".into(),
+			flag_min_gas_price: Some("".into()),
 			flag_usd_per_tx: "0.0025".into(),
 			flag_usd_per_eth: "auto".into(),
 			flag_price_update_period: "hourly".into(),
@@ -1035,6 +1039,7 @@ mod tests {
 				reseal_max_period: Some(60000),
 				work_queue_size: None,
 				relay_set: None,
+				min_gas_price: None,
 				usd_per_tx: None,
 				usd_per_eth: None,
 				price_update_period: Some("hourly".into()),

parity/cli/presets/config.dev.toml

@@ -0,0 +1,6 @@
+[parity]
+chain = "dev"
+
+[mining]
+reseal_min_period = 0
+min_gas_price = "0"

parity/cli/presets/mod.rs

@@ -16,8 +16,7 @@
 
 pub fn preset_config_string(arg: &str) -> Result<&'static str, &str> {
     match arg.to_lowercase().as_ref() {
-        "poa" => Ok(include_str!("./config.poa.toml")),
-        "pow" => Ok(include_str!("./config.pow.toml")),
+        "dev" => Ok(include_str!("./config.dev.toml")),
         _ => Err(arg.clone())
     }
 }

parity/cli/usage.txt

@@ -295,6 +295,10 @@ Sealing/Mining Options:
                                    means we relay nothing if not mining);
                                    lenient - Same as strict when mining, and cheap
                                    when not (default: {flag_relay_set}).
+  --min-gas-price STRING           Minimum amount of Wei per GAS to be paid for a
+                                   transaction to be accepted for mining. Overrides
+                                   --basic-tx-usd.
+                                   (default: {flag_min_gas_price:?})
   --usd-per-tx USD                 Amount of USD to be paid for a basic transaction
                                    (default: {flag_usd_per_tx}). The minimum gas price is set
                                    accordingly.