clear sigprocmask on start
clear sigprocmask on start

if sigprocmask is not cleared some signals might be blocked from
parent/execve. This is the case for for upgrades where we execve in the
signal handler. As a consequence, upgrading twice doesn't work

StephanDollberg/yotta,StephanDollberg/yotta,StephanDollberg/yotta,StephanDollberg/yotta,StephanDollberg/yotta