oeqa/selftest/debuginfod: use localpkgfeed to speed server startup

Sometimes the debuginfod selftest fails due to a timeout, because it
spends too long scanning a huge deploy directory that due to what tests
were ran previously can contain 30K packages.

The test only needs a subset of the feed, so use the new localpkgfeed
class to construct a minimal feed before running the test.

[ YOCTO #14937 ]

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 855376f5)
Signed-off-by: Steve Sakoman <steve@sakoman.com>