[activity.py] Identify Gerrit-style bug annotations in commit messages

Extract bug numbers noted "Bug: 99999" in addition to the older
"BUG=99999" style.

Bug: None
Change-Id: If29139ee2bae3c515748395a846e45ce6995d9ec
Reviewed-on: https://chromium-review.googlesource.com/548718Reviewed-by: Marc-Antoine Ruel <maruel@chromium.org>
Commit-Queue: Nicolas Dossou-Gbété <dgn@chromium.org>

my_activity.py

@@ -265,7 +265,10 @@ class MyActivity(object):
 
     bugs = []
     if description:
-      matches = re.findall('BUG=(((\d+)(,\s?)?)+)', description)
+      # Handle both "Bug: 99999" and "BUG=99999" bug notations
+      # Multiple bugs can be noted on a single line or in multiple ones.
+      matches = re.findall(r'BUG[=:]\s?(((\d+)(,\s?)?)+)', description,
+                           flags=re.IGNORECASE)
       if matches:
         for match in matches:
           bugs.extend(match[0].replace(' ', '').split(','))