Implement susped, resume and cancel for the Postinstall action.

This patch sends SIGSTOP/SIGCONT to the running postinstall program to
suspend/resume the child process, and SIGKILL when cancelling it.

Bug: 27272144
TEST=Added unittest to check the signal being sent.

(cherry picked from commit d15c546ed794293d0a63770467a0f3c4c84c6214)

Change-Id: Ie99b406b4d7f73dda4189b7a5a7d627c866055d6
diff --git a/Android.mk b/Android.mk
index 0d9338d..cf1310a 100644
--- a/Android.mk
+++ b/Android.mk
@@ -709,7 +709,7 @@
 $(call ue-unittest-sample-image,disk_ext2_1k.img)
 $(call ue-unittest-sample-image,disk_ext2_4k.img)
 $(call ue-unittest-sample-image,disk_ext2_4k_empty.img)
-$(call ue-unittest-sample-image,disk_ext2_ue_settings.img)
+$(call ue-unittest-sample-image,disk_ext2_unittest.img)
 
 # test_http_server (type: executable)
 # ========================================================
@@ -745,7 +745,7 @@
     ue_unittest_disk_ext2_1k.img \
     ue_unittest_disk_ext2_4k.img \
     ue_unittest_disk_ext2_4k_empty.img \
-    ue_unittest_disk_ext2_ue_settings.img
+    ue_unittest_disk_ext2_unittest.img
 LOCAL_MODULE_CLASS := EXECUTABLES
 LOCAL_CPP_EXTENSION := .cc
 LOCAL_CLANG := true