adb: move all cleanup to a function with defined ordering.

We want to explicitly define the order in which we teardown adb, so
move all of the at_quick_exits sprinkled throughout into one function
containing all of the cleanup functions.

Bug: http://b/37104408
Test: adb kill-server; adb start-server
Change-Id: I394f5782eb147e394d4b87df1ba364c061de4b90
diff --git a/usb.h b/usb.h
index e867ec8..f428ede 100644
--- a/usb.h
+++ b/usb.h
@@ -22,6 +22,7 @@
 
 #define ADB_USB_INTERFACE(handle_ref_type)                       \
     void usb_init();                                             \
+    void usb_cleanup();                                          \
     int usb_write(handle_ref_type h, const void* data, int len); \
     int usb_read(handle_ref_type h, void* data, int len);        \
     int usb_close(handle_ref_type h);                            \