dev-manual: Updated the "Making Images More Secure" section.

Fixes [YOCTO #5482]

I did some significant re-writing and re-organization of this
section.  It now includes a bit about securing an image in general,
provides general considerations, considerations specific to the
OpenEmbedded build system, pointers to some tools in meta-security
layer, and some other items.

I added some key references to the section on considerations
specific to the OpenEmbedded build system.  In particular, I
provided some cross-linking back to the extrausers.bbclass
section to reference an example of adding a user account.  I
also split out the topics of adding an extra user and setting
a password on the image in the bulleted list.

Updated the setting root and extra user's passwords.  Also,
permanently removed the reference to the wiki that showed the
less optimal way of setting a root password.

Added a cross-reference to the meta-selinux layer in the section
that describes how to make images more secure.

(From yocto-docs rev: 812bf8e2c91c4dd14a2245509ea7008a24e90835)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
file: add wrapper to nativesdk-file

Backport commit 69a3ab3 to 'daisy' which uses a different version of
file package.

Author of the original patch: Hongxu Jia <hongxu.jia@windriver.com>

(From OE-Core rev: 4bd4da1e1433ae64720f59d48188ecd1960dac28)

Signed-off-by: Javier Viguera <javier.viguera@digi.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>