Show $ADB_VENDOR_KEYS if authentication fails.

Incorrectly set $ADB_VENDOR_KEYS is the most likely cause of failed
adb connections. Make it easier to debug such problems by including
the value in use in the error message.

Bug: 20165551
Change-Id: I64c1d98ae6d3fb40eea9e1f0ddcfcf4f2d9d7318
diff --git a/adb.cpp b/adb.cpp
index ad85184..b09e853 100644
--- a/adb.cpp
+++ b/adb.cpp
@@ -838,10 +838,10 @@
             }
         }
 
-        const char* err;
-        transport = acquire_one_transport(CS_ANY, ttype, serial, &err);
+        std::string error_msg;
+        transport = acquire_one_transport(CS_ANY, ttype, serial, &error_msg);
         if (!transport) {
-            sendfailmsg(reply_fd, err);
+            sendfailmsg(reply_fd, error_msg.c_str());
             return 1;
         }
 
@@ -910,14 +910,14 @@
             serial = service;
         }
 
-        const char* error_string = "unknown failure";
-        transport = acquire_one_transport(CS_ANY, type, serial, &error_string);
+        std::string error_msg = "unknown failure";
+        transport = acquire_one_transport(CS_ANY, type, serial, &error_msg);
 
         if (transport) {
             s->transport = transport;
             adb_write(reply_fd, "OKAY", 4);
         } else {
-            sendfailmsg(reply_fd, error_string);
+            sendfailmsg(reply_fd, error_msg.c_str());
         }
         return 1;
     }
@@ -975,7 +975,7 @@
     if(!strncmp(service,"get-serialno",strlen("get-serialno"))) {
         const char *out = "unknown";
         transport = acquire_one_transport(CS_ANY, ttype, serial, NULL);
-       if (transport && transport->serial) {
+        if (transport && transport->serial) {
             out = transport->serial;
         }
         send_msg_with_okay(reply_fd, out, strlen(out));
@@ -984,7 +984,7 @@
     if(!strncmp(service,"get-devpath",strlen("get-devpath"))) {
         const char *out = "unknown";
         transport = acquire_one_transport(CS_ANY, ttype, serial, NULL);
-       if (transport && transport->devpath) {
+        if (transport && transport->devpath) {
             out = transport->devpath;
         }
         send_msg_with_okay(reply_fd, out, strlen(out));