dropbear: Fix upstart script to respect /etc/default/dropbear

* https://bugzilla.yoctoproject.org/show_bug.cgi?id=2578 fixes dropbear
  exploiting IMAGE_FEATURES incorrectly and moves password-less option
  (enabled with debug-tweaks IMAGE_FEATURE) to runtime config instead of
  hardcoding it in dropbear binary.
* our upstart script wasn't respecting this new config, fix that

[GF-4354] Upgrade to Yocto 1.4 Dylan
[GF-5571] CCC: Upgrade to Yocto 1.4 Dylan

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: I87cd812448d10846a4515c59184991fc5e0970e7
Reviewed-on: https://g2g.palm.com/2239
Reviewed-by: Martin Jansa <Martin.Jansa@lge.com>
Tested-by: Martin Jansa <Martin.Jansa@lge.com>
Reviewed-by: Build Verification
Reviewed-by: Steve Lemke <steve.lemke@lge.com>
Reviewed-by: Herb Kuta <herb.kuta@lge.com>
Reviewed-by: Susan Montooth <susan.montooth@lge.com>