update-ref: add test cases for bare repository

update-ref: add test cases for bare repository

The default behavior of update-ref to create reflogs differs in
repositories with worktree and bare ones. The existing tests cover only
the behavior of repositories with worktree.

This commit adds tests that assert the correct behavior in bare
repositories for update-ref. Two cases are covered:

 - If core.logAllRefUpdates is not set, no reflogs should be created
 - If core.logAllRefUpdates is true, reflogs should be created

Signed-off-by: Cornelius Weig <cornelius.weig@tngtech.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>