lib/oe/package_manager: Include PACKAGE_FEED_PREFIX instead of hardcode paths

lib/oe/package_manager: Include PACKAGE_FEED_PREFIX instead of hardcode paths

Instead of hardcode paths (/rpm/, /ipk/, /deb/), use a user-defined prefix
when creating the URI feeds. URIs now will have the following syntax:

    PACKAGE_FEED_URIS_1/PACKAGE_FEED_PREFIX
    PACKAGE_FEED_URIS_2/PACKAGE_FEED_PREFIX
    .

where PACKAGE_FEED_URIS = "PACKAGE_FEED_URIS_1 PACKAGE_FEED_URIS_2 ...."

[YOCTO #5407]

Signed-off-by: Leonardo Sandoval <leonardo.sandoval.gonzalez@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>