Change the logic to check the cert exchange is needed or not

Summary:
It has been seen [here](https://fb.workplace.com/groups/flippersupport/permalink/1094276434386347/) that the user's app sandbox can be in a state where it might not have the device id information, but other app certificates. This causes the issue of "Timed out waiting for unknown device".

We get the deviceid from flipper into app's sandbox when cert exchange happens. So if we don't have the device id information, we can again redo the cert exchange to get the sandbox in a state where flipper connects. Thus I updated the logic of `hasRequiredFiles` which checks the required files for cert exchange.

Reviewed By: mweststrate

Differential Revision: D27265693

fbshipit-source-id: ccf311f4728837ee9385c95c38f94c9c93380feb

xplat/Flipper/ConnectionContextStore.cpp

@@ -37,8 +37,10 @@ bool ConnectionContextStore::hasRequiredFiles() {
       loadStringFromFile(absoluteFilePath(CLIENT_CERT_FILE_NAME));
   std::string privateKey =
       loadStringFromFile(absoluteFilePath(PRIVATE_KEY_FILE));
+  std::string config =
+      loadStringFromFile(absoluteFilePath(CONNECTION_CONFIG_FILE));
 
-  if (caCert == "" || clientCert == "" || privateKey == "") {
+  if (caCert == "" || clientCert == "" || privateKey == "" || config == "") {
     return false;
   }
   return true;