pseudo 1.8.1 doesn't work with docker & dumb-init

[wenzong fan <wenzong.fan@windriver.com>]

Hi Experts,

While I trying to build Yocto in Docker Container which using dumb-init 
as init system, I found the build always be stopped at some point and 
the container was terminated as well with below errors:

     Child process timeout after 2 seconds.
     Child process exit status 4: lock_held

Sometimes there's not any obvious error message.

After some `git bisect` testing, I believe the issue was started since 
commit:

----------------------
9df3cdf42d8c1216682f497f0b166a43ef9f4184 is the first bad commit
commit 9df3cdf42d8c1216682f497f0b166a43ef9f4184
Author: Richard Purdie <richard.purdie@linuxfoundation.org>
Date: Tue Jul 5 13:18:31 2016 +0100

     pseudo: Upgrade to 1.8.1

     * Drop patches where the changes exist upstream
     * Fetch from git as no tarball is available for 1.8.1
     * Move common code to pseudo.inc
     * Update patchset in git recipe

     (From OE-Core rev: 0c36984d4c501d12fa91cf7371511641585cc256)
-----------------------

Finally I narrowed it down to pseudo commit:

------------------------
commit 77ee254a6c974aad9bcab2c58c9ee9e0880c9718
Author: Peter Seebach <peter.seebach@windriver.com>
Date: Tue Mar 1 16:21:15 2016 -0600

     Server launch reworking.

     This is the big overhaul to have the server provide meaningful exit 
status
     to clients.

     In the process, I discovered that the server was running with 
signals blocked
     if launched by a client, which is not a good thing, and prevented 
this from
     working as intended.

     Still looking to see why more than one server spawn seems to happen.
------------------------

I also created a testcase for reproducing the issue at:

     https://github.com/WenzongFan/docker-build-yocto

For dumb-init please refer to:

     https://github.com/Yelp/dumb-init

Could anyone help to fix the signal handling in pseudo?


Thanks
Wenzong