t1507: assert output of rev-parse

t1507: assert output of rev-parse

Tests in t1507-rev-parse-upstream.sh compare files "expect" and "actual"
to assert the output of "git rev-parse", "git show", and "git log".
However, two of the tests '@{reflog}-parsing does not look beyond colon'
and '@{upstream}-parsing does not look beyond colon' don't inspect the
contents of the created files.

Assert output of "git rev-parse" in tests in t1507-rev-parse-upstream.sh
to improve test coverage.

Signed-off-by: Andrei Rybak <rybak.a.v@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>