Updated online/offline event checks so they are run during initialisation.

Changed the online event to `once` and set it to be bound every time the node goes offline.

The above changes handle the case where:
1) `embark run` runs and starts geth.
2) geth is killed manually
3) `embark blockchain` is run in separate process to restart geth
4) the `embark run` process detects this change and restarts the web3 provider and recompiles/deploys/builds

Every time `embark blochain` is restarted, an error is appended and all are emitted from the `eth-block-tracker`. This is a bug but can't figure out where it originates. The downside is that if, for example, `embark blockchain` is restarted 4 times, there will be 4 errors emitted from the `eth-block-tracker`. Because of this, errors emitted from `eth-block-tracker` have been reduced to trace to avoid clogging the logs.

lib/cmds/blockchain/blockchain.js

@@ -183,7 +183,7 @@ Blockchain.prototype.run = function() {
       console.log('Geth: ' + data);
     });
     self.child.on('exit', (code) => {
-      let strCode = '';
+      let strCode;
       if (code) {
         strCode = ' with error code ' + code;
       } else {

lib/contracts/blockchain.js

@@ -73,6 +73,20 @@ class Blockchain {
           if (!err) {
             self.isWeb3Ready = true;
             self.events.emit(WEB3_READY);
+            // if the ethereum node goes offline, we need a check to ensure
+            // the provider is also stopped
+            self.events.on('check:wentOffline:Ethereum', () => {
+              self.logger.trace('Ethereum went offline: stopping web3 provider...');
+              self.provider.stop();
+              
+              // once the node goes back online, we can restart the provider
+              self.events.once('check:backOnline:Ethereum', () => {
+                self.logger.trace('Ethereum back online: starting web3 provider...');
+                self.provider.startWeb3Provider(() => {
+                  self.logger.trace('web3 provider restarted after ethereum node came back online');
+                });
+              });
+            });
             return next();
           }
           self.web3StartedInProcess = true;
@@ -161,14 +175,6 @@ class Blockchain {
         if (err && err !== NO_NODE) {
           return cb(err);
         }
-        else if ((statusObj && statusObj.status === 'off') || err === NO_NODE){
-          self.provider.stop();
-          self.events.on('check:backOnline:Ethereum', () => {
-            self.provider.startWeb3Provider(() => {
-              self.logger.trace('web3 provider restarted after ethereum node came back online');
-            });
-          });
-        }
         cb(statusObj);
       });
     }, 5000, 'off');

lib/contracts/provider.js

@@ -39,8 +39,12 @@ class Provider {
 
     // network connectivity error
     self.engine.on('error', (err) => {
-      // report connectivity errors
-      self.logger.error(err);
+      // report connectivity errors as trace due to polling
+      self.logger.trace('web3 provider error: ', err);
+      self.logger.trace('stopping web3 provider due to error');
+      
+      // prevent continuous polling errors
+      self.engine.stop();
     });
 
     self.engine.start();