Add more error regexps for git retry

BUG=

Review-Url: https://codereview.chromium.org/2165643002
diff --git a/git_common.py b/git_common.py
index 289665e..c602103 100644
--- a/git_common.py
+++ b/git_common.py
@@ -92,6 +92,12 @@
     # crbug.com/430343
     # TODO(dnj): Resync with Chromite.
     r'The requested URL returned error: 5\d+',
+
+    r'Connection reset by peer',
+
+    r'Unable to look up',
+
+    r'Couldn\'t resolve host',
 )
 
 GIT_TRANSIENT_ERRORS_RE = re.compile('|'.join(GIT_TRANSIENT_ERRORS),