update-alternatives: Add a build-time dependency

update-alternatives: Add a build-time dependency

We need to add a build time dependency on virtual/update-alternatives,
however we can't just do DEPENDS +=, or we end up with various problems.  To
work around this, in the anonymous python space we ensure we only do the
addition when the package does not provide virtual/update-alternatives and
it is a target package.

Also the system wide PREFERRED_PROVIDER was incorrect.  It references a
runtime package, and not the recipe it should have.  This has been corrected.

[YOCTO #3691]

(From OE-Core rev: 56a59ef12936dcc6464cf1d43dda6957a5aa8c65)

Signed-off-by: Mark Hatle <mark.hatle@windriver.com>
Tested-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>