wt-status.c: set the committable flag in the collect phase

wt-status.c: set the committable flag in the collect phase

In an update to fix a bug with "commit --dry-run" it was found that
the committable flag was broken. The update was, at the time, accepted
as it was better than the previous version. [1]

Since the setting of the committable flag had been done in
wt_longstatus_print_updated, move it to wt_status_collect_updated_cb.

Set the committable flag in wt_status_collect_changes_initial to keep
from introducing a rebase regression.

Instead of setting the committable flag in show_merge_in_progress, in
wt_status_cllect check for a merge that has not been committed. If
present then set the committable flag.

Change the tests to expect success since updates to the wt-status
broken code section is being fixed.

[1] https://public-inbox.org/git/xmqqr3gcj9i5.fsf@gitster.mtv.corp.google.com/

Signed-off-by: Stephen P. Smith <ischis2@cox.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>