t: make test-bloom initialize repository

t: make test-bloom initialize repository

The bloom filter code relies on reading object IDs using parse_oid_hex.
In order to make that work with an appropriate size, we need to have
initialized the repository's hash algorithm.  Since the values we're
processing depend on the repository in use, let's set up the repository
when we run the test helper.

Signed-off-by: brian m. carlson <redacted>
Reviewed-by: Eric Sunshine <redacted>
Signed-off-by: Junio C Hamano <redacted>