Alter comments left on 'Related' bugs

Avoid posting confusing 'Fix proposed' or 'Fix merged' comments for
'Related' bugs.

This also fixes a latent bug (the 'add_comment' task was not really
taken into consideration before actually adding a comment).

Fixes bug: #1218044

Change-Id: Ic287050cf5dcf690239484038fb957e897df886f
Merge "Alter comments left on 'Related' bugs"