commitpkg: use absolute paths when uploading files

This fixes a problem where rsync won't work if the pkgver contains a
colon (epoch). In this case rsync assumes that the colon is a
remote:path separator and having src and dest both being remote
arguments is not supported.

Signed-off-by: Florian Pritz <bluewind@xinu.at>
Signed-off-by: Pierre Schmitz <pierre@archlinux.de>