specdep: Add '--ignore-from' argument

specdep.py --ignore-from ignore.txt SPECS/*.spec prints the
dependencies of the supplied spec files, but ignores any
package names in ignore.txt

Signed-off-by: Euan Harris <euan.harris@citrix.com>
specdep: --ignore-from should remove newlines in ignore file

Otherwise the names don't match. To make it clear what has been
ignored, we now emit comments into the deps output.

Signed-off-by: David Scott <dave.scott@citrix.com>
configure: detect the distro and use a pre-configured ignore-file

If a specific distro ignore file exists then we use it, otherwise
we fall back to a default list.

The actual ignore file in use is a symlink called 'ignore'.

Signed-off-by: David Scott <dave.scott@citrix.com>
trusty: don't build libnl3

Signed-off-by: David Scott <dave.scott@citrix.com>