Bug 874729 - Part 1: Swallow IOErrors when pulling ANR traces. r=jmaher

On my local testing devices, |adb pull| complains about not being able
to read /data/anr/traces.txt but the command succeeds.  The subsequent
local file read produces an IOError.  This ignores that exception.

build/mobile/remoteautomation.py

@@ -126,7 +126,8 @@ class RemoteAutomation(Automation):
                 self.deleteANRs()
             except DMError:
                 print "Error pulling %s" % traces
-                pass
+            except IOError:
+                print "Error pulling %s" % traces
         else:
             print "%s not found" % traces