test: Show setup/image-prepare timings in CI

Our log viewer shows how long every test takes, but the
"initialization" step has no timing information. To make better guesses
on what to optimize add two timings for the "setup" step which pulls
bots and pixels, and for image-prepare itself.

The idea is that the logs viewer would maybe show these steps as
sections with timing information.

test/run

@@ -17,9 +17,9 @@
 
 set -eu
 
-cat /proc/meminfo
-
-grep -r . /sys/kernel/mm/ksm/
+if [ -n "${TEST_REVISION:-}" ]; then
+    START_TIME=$SECONDS
+fi
 
 test/common/make-bots
 
@@ -87,11 +87,15 @@ if [ -n "$TEST_SCENARIO" ] && [ -z "$RUN_OPTS" ]; then
     echo "Unknown test scenario: $TEST_SCENARIO"
     exit 1
 fi
+if [ -n "${TEST_REVISION:-}" ]; then
+    echo "SETUP DONE $((SECONDS - START_TIME))s"
+    PREPARE_START=$SECONDS
+fi
 
 test/image-prepare --verbose ${PREPARE_OPTS} "$TEST_OS"
+if [ -n "${TEST_REVISION:-}" ]; then
+    echo "PREPARE DONE $((SECONDS - PREPARE_START))s"
+    TESTS_START=$SECONDS
+fi
 test/common/run-tests --test-dir test/verify --track-naughties ${RUN_OPTS}
-
-grep -H . /sys/kernel/mm/ksm/pages_{shared,sharing,unshared}
-awk '{print $1 * 4 / 1024 " MB saved"}' /sys/kernel/mm/ksm/pages_sharing
-grep -r . /sys/kernel/mm/ksm/
-cat /proc/meminfo
+echo "SETUP DONE $((SECONDS - TESTS_START))s"