debuggerd_client: properly wait for completion.

Use an intermediate pipe to detect and report when a requested dump has
completed.

Bug: http://b/35241370
Bug: http://b/35813071
Test: debuggerd_test
Test: manually triggered a background ANR
Change-Id: If14aedf6071288360f1a7853d5a2ee79db121759
diff --git a/debuggerd/Android.bp b/debuggerd/Android.bp
index 2d6c7f5..024bc3d 100644
--- a/debuggerd/Android.bp
+++ b/debuggerd/Android.bp
@@ -161,6 +161,7 @@
     target: {
         android: {
             srcs: [
+                "client/debuggerd_client_test.cpp",
                 "debuggerd_test.cpp",
                 "util.cpp"
             ],
@@ -171,6 +172,7 @@
         "libbacktrace",
         "libbase",
         "libcutils",
+        "libdebuggerd_client",
     ],
 
     static_libs: [