profiler: update retry command used in E2E test to backoff after failed attempts

Change-Id: Ia24b521f702c21d0042887ad2aec8f47b6899c07
Reviewed-on: https://code-review.googlesource.com/c/gocloud/+/56670
Reviewed-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Kalyana Chadalavada <kchadalavada@google.com>
diff --git a/profiler/proftest/proftest.go b/profiler/proftest/proftest.go
index d4c8ca1..ffc6a94 100644
--- a/profiler/proftest/proftest.go
+++ b/profiler/proftest/proftest.go
@@ -56,6 +56,7 @@
 
 retry() {
   for i in {1..3}; do
+    [ $i == 1 ] || sleep 10  # Backing off after a failed attempt.
     "${@}" && return 0
   done
   return 1