adb: Recognize rescue mode.

This CL adds client support to recognize the rescue mode (which will be
served by recovery image). It also allows waiting for a device to enter
rescue mode. The support for the actual rescue commands will be added in
follow-up CLs.

Bug: 128415917
Test: `adb devices` recognizes devices under rescue mode.
Test: `adb wait-for-rescue` waits for device to be in rescue mode.
Change-Id: I367d7339fe68006aba09a1e3db6370d472296676
diff --git a/adb/client/commandline.cpp b/adb/client/commandline.cpp
index 43a3e5e..f25955d 100644
--- a/adb/client/commandline.cpp
+++ b/adb/client/commandline.cpp
@@ -190,7 +190,7 @@
         "scripting:\n"
         " wait-for[-TRANSPORT]-STATE\n"
         "     wait for device to be in the given state\n"
-        "     STATE: device, recovery, sideload, bootloader, or disconnect\n"
+        "     STATE: device, recovery, rescue, sideload, bootloader, or disconnect\n"
         "     TRANSPORT: usb, local, or any [default=any]\n"
         " get-state                print offline | bootloader | device\n"
         " get-serialno             print <serial-number>\n"
@@ -1037,11 +1037,12 @@
     }
 
     if (components[3] != "any" && components[3] != "bootloader" && components[3] != "device" &&
-        components[3] != "recovery" && components[3] != "sideload" &&
+        components[3] != "recovery" && components[3] != "rescue" && components[3] != "sideload" &&
         components[3] != "disconnect") {
         fprintf(stderr,
                 "adb: unknown state %s; "
-                "expected 'any', 'bootloader', 'device', 'recovery', 'sideload', or 'disconnect'\n",
+                "expected 'any', 'bootloader', 'device', 'recovery', 'rescue', 'sideload', or "
+                "'disconnect'\n",
                 components[3].c_str());
         return false;
     }