specdep: Extract specfile-handling code to a library

Signed-off-by: Euan Harris <euan.harris@citrix.com>
specdep: Return package paths from library

RPM already gives us paths for package files - previously
we were removing these and then adding them back on when
we wrote the Makefile.

Signed-off-by: Euan Harris <euan.harris@citrix.com>
specdep: Add 'specpath' to spec object

This gets rid of more needless path joining.

Signed-off-by: Euan Harris <euan.harris@citrix.com>
specdep: Remove unnecessary extra iteration over packages

Signed-off-by: Euan Harris <euan.harris@citrix.com>
specdep: Move CHROOT_DIST to pkg library

Signed-off-by: Euan Harris <euan.harris@citrix.com>
specdep: Move download URL handling to library

Signed-off-by: Euan Harris <euan.harris@citrix.com>
specdep: Move specs and ignore list to command line arguments

Signed-off-by: Euan Harris <euan.harris@citrix.com>
specdep: Move build recipes into the Makefile

Signed-off-by: Euan Harris <euan.harris@citrix.com>
pkg: Remove 'packages()' method

Signed-off-by: Euan Harris <euan.harris@citrix.com>
specdep/pkg: Add back Debian dependency generation

Signed-off-by: Euan Harris <euan.harris@citrix.com>