Extract getBlhostCmd() to shared.js

scripts/shared.js

@@ -1,5 +1,26 @@
 require('shelljs/global');
 
+function getBlhostCmd() {
+    let blhostPath;
+    switch (process.platform) {
+        case 'linux':
+            blhostPath = 'linux/amd64/blhost';
+            break;
+        case 'darwin':
+            blhostPath = 'mac/blhost';
+            break;
+        case 'win32':
+            blhostPath = 'win/blhost.exe';
+            break;
+        default:
+            echo('Your operating system is not supported');
+            exit(1);
+            break;
+    }
+
+    return `../../../lib/bootloader/bin/Tools/blhost/${blhostPath} --usb 0x1d50,0x6121`;
+}
+
 function execRetry(command) {
     let firstRun = true;
     let remainingRetries = 3;
@@ -16,7 +37,8 @@ function execRetry(command) {
 }
 
 const exp = {
-    execRetry
+    getBlhostCmd,
+    execRetry,
 }
 
 Object.keys(exp).forEach(function (cmd) {