Switch fastboot/init/libprocessgroup to std::this_thread::sleep_for.

Bug: http://b/32878766
Test: boots
Change-Id: Ie0ddfb7e60f2da5f6eefbb10c83a92e88c137ae3
diff --git a/init/util.cpp b/init/util.cpp
index bde4efb..cb5a094 100644
--- a/init/util.cpp
+++ b/init/util.cpp
@@ -34,6 +34,8 @@
 #include <sys/types.h>
 #include <sys/un.h>
 
+#include <thread>
+
 #include <android-base/file.h>
 #include <android-base/logging.h>
 #include <android-base/stringprintf.h>
@@ -326,7 +328,7 @@
         struct stat sb;
         if (stat(filename, &sb) != -1) return 0;
 
-        usleep(10000);
+        std::this_thread::sleep_for(10ms);
     }
     return -1;
 }