Open database connection with 'w' instead of 'r' for writing

Summary:
there are several places we open an 'r' connection but use it
for writing. Fix them.

Test Plan:
ran parse_one_commit.php against one revision which executes
the code with problem. It used to throw exception. Now it works fine.

Reviewed By: Girish
Reviewers: tuomaspelkonen, Girish
Commenters: aran
CC: aran, Girish
Differential Revision: 213

scripts/repository/rebuild_summaries.php

@@ -27,7 +27,7 @@ PhutilSymbolLoader::loadClass('PhabricatorRepositoryCommit');
 
 $commit = new PhabricatorRepositoryCommit();
 
-$conn_w = id(new PhabricatorRepository())->establishConnection('r');
+$conn_w = id(new PhabricatorRepository())->establishConnection('w');
 $sizes = queryfx_all(
   $conn_w,
   'SELECT repositoryID, count(*) N FROM %T GROUP BY repositoryID',

src/applications/repository/daemon/commitdiscovery/base/PhabricatorRepositoryCommitDiscoveryDaemon.php

@@ -76,7 +76,7 @@ abstract class PhabricatorRepositoryCommitDiscoveryDaemon
       $event->recordEvent();
 
       queryfx(
-        $repository->establishConnection('r'),
+        $repository->establishConnection('w'),
         'INSERT INTO %T (repositoryID, size, lastCommitID, epoch)
           VALUES (%d, 1, %d, %d)
           ON DUPLICATE KEY UPDATE

src/applications/repository/worker/commitmessageparser/base/PhabricatorRepositoryCommitMessageParserWorker.php

@@ -51,7 +51,7 @@ abstract class PhabricatorRepositoryCommitMessageParserWorker
       if ($revision) {
 
         queryfx(
-          $revision->establishConnection('r'),
+          $revision->establishConnection('w'),
           'INSERT IGNORE INTO %T (revisionID, commitPHID) VALUES (%d, %s)',
           DifferentialRevision::TABLE_COMMIT,
           $revision->getID(),