adb: retry connecting disconnected emulators instead of always looping.

Previously we loop through local ports every second, this patch improves
the strategy by retrying only just disconnected emulators.

Bug: 26468076
Bug: 19974213
Bug: 22920867

Change-Id: I43ccb746922d104202b0f81a3d163d850bbc890e
diff --git a/adb/transport.cpp b/adb/transport.cpp
index 55082a5..65b05b8 100644
--- a/adb/transport.cpp
+++ b/adb/transport.cpp
@@ -952,6 +952,8 @@
     for (const auto& transport : pending_list) {
         if (transport->serial && strcmp(serial, transport->serial) == 0) {
             adb_mutex_unlock(&transport_lock);
+            VLOG(TRANSPORT) << "socket transport " << transport->serial
+                << " is already in pending_list and fails to register";
             delete t;
             return -1;
         }
@@ -960,6 +962,8 @@
     for (const auto& transport : transport_list) {
         if (transport->serial && strcmp(serial, transport->serial) == 0) {
             adb_mutex_unlock(&transport_lock);
+            VLOG(TRANSPORT) << "socket transport " << transport->serial
+                << " is already in transport_list and fails to register";
             delete t;
             return -1;
         }
@@ -992,8 +996,7 @@
 void kick_all_tcp_devices() {
     adb_mutex_lock(&transport_lock);
     for (auto& t : transport_list) {
-        // TCP/IP devices have adb_port == 0.
-        if (t->type == kTransportLocal && t->adb_port == 0) {
+        if (t->IsTcpDevice()) {
             // Kicking breaks the read_transport thread of this transport out of any read, then
             // the read_transport thread will notify the main thread to make this transport
             // offline. Then the main thread will notify the write_transport thread to exit.