adb: add `adb reconnect offline` to reconnect offline devices.

Add a command to reconnect offline/unauthorized devices, mainly for use
with the inotify-monitoring of vendor key directories added by 2e671202.

Bug: http://b/29273531
Test: manually tested with a sailfish + copying vendor keys
Change-Id: If34cccee4ae553ada65d128b57d03cba8c0d7c46
diff --git a/adb/commandline.cpp b/adb/commandline.cpp
index 1f03c1a..e15bcad 100644
--- a/adb/commandline.cpp
+++ b/adb/commandline.cpp
@@ -1950,10 +1950,17 @@
     } else if (!strcmp(argv[0], "reconnect")) {
         if (argc == 1) {
             return adb_query_command("host:reconnect");
-        } else if (argc == 2 && !strcmp(argv[1], "device")) {
-            std::string err;
-            adb_connect("reconnect", &err);
-            return 0;
+        } else if (argc == 2) {
+            if (!strcmp(argv[1], "device")) {
+                std::string err;
+                adb_connect("reconnect", &err);
+                return 0;
+            } else if (!strcmp(argv[1], "offline")) {
+                std::string err;
+                return adb_query_command("host:reconnect-offline");
+            } else {
+                return usage();
+            }
         }
     }