Measure seconds since last push directly

Don't push the datetime as a metric, since that's annoying to parse and
process in Grafana.

"waittime" is the time between push and pick-up for pr_processing events, and
time time between push and check completion for pr_processing_done events.

ci/build-helpers.sh

@@ -45,7 +45,7 @@ function report_state () {
                 ${NUM_BASE_COMMITS:+"num_base_commits=$NUM_BASE_COMMITS"} \
                 -- "host=\"$(hostname -s)\"" "state=\"$current_state\"" \
                 "prid=\"$PR_NUMBER\"" ${prtime:+prtime=$prtime} ${PR_OK:+prok=$PR_OK} \
-                ${LAST_PUSH_TIME:+push=$LAST_PUSH_TIME} \
+                ${LAST_PUSH_TIME:+waittime=$((time_now - LAST_PUSH_TIME))} \
                 ${HAVE_JALIEN_TOKEN:+have_jalien_token=$HAVE_JALIEN_TOKEN}
 
   # Push to Google Analytics if configured

list-branch-pr

@@ -24,6 +24,7 @@ import sys
 
 from argparse import ArgumentParser
 from collections import defaultdict
+from datetime import datetime
 
 from gql import Client, gql
 from gql.transport.requests import RequestsHTTPTransport
@@ -179,16 +180,15 @@ class RepoConfig:
                 ("succeeded" if success else "failed")
         else:
             state = "skip"
-        print("pr: {number:6d}@{sha:.7s}: revd={reviewed:d} trust={trust:d} "
-              "tested={tested:d} success={success:d} => state={state}".format(
-                  number=pull_number, sha=commit_hash, reviewed=reviewed,
-                  trust=is_trusted, tested=tested, success=success, state=state
-              ), file=sys.stderr)
+        updated_time = last_commit["pushedDate"]
+        print(f"pr: {pull_number:6d}@{commit_hash:.7s}: upd={updated_time:s} "
+              f"revd={reviewed:d} trust={is_trusted:d} tested={tested:d} "
+              f"success={success:d} => state={state}", file=sys.stderr)
         return None if state == "skip" else (state, {
             "number": pull_number,
             "sha": commit_hash,
             "build_config": self.build_config,
-            "updated_at": last_commit["pushedDate"],
+            "updated_at": updated_time,
         })
 
     def process_pulls(self, session, repo_info, show_base_branch=False):
@@ -258,8 +258,11 @@ def main(args):
         # pr["updated_at"] can apparently be None sometimes, which breaks
         # sorting, so default to the empty string if so.
         for pull in sorted(prs, key=lambda pr: pr["updated_at"] or ""):
-            print(group, pull["number"], pull["sha"],
-                  pull["build_config"], pull["updated_at"], sep="\t")
+            last_push_timestamp = \
+                int(datetime.fromisoformat(pull["updated_at"]).timestamp) \
+                if pull["updated_at"] else int(datetime.utcnow().timestamp)
+            print(group, pull["number"], pull["sha"], pull["build_config"],
+                  last_push_timestamp, sep="\t")
 
     if grouped["untested"]:
         # If there are untested PRs waiting, build all of them first.