test-history: Skip test if we cannot read from the Journal

[smcv]

In some OS configurations, unprivileged users cannot read back messages
that they have written to the system log. This test cannot succeed if that
happens, so skip it.

In particular, if the Journal is only in-memory rather than persisted
to disk (as it was by default in Debian 10), then there are no per-user
Journal files, only a single system-wide Journal which requires privileges
to read.

[smcv]

This fixes 8b05f6b "Add a unit test for the history command", so should be cherry-picked to 1.12.x and 1.10.x.

[mwleeds]

Looks good other than the comment above, and shellcheck doesn't find anything new to complain about. It's a little strange that journalctl needs --user but the logger command doesn't have a corresponding option, but I take your word for it that it's correct.

[smcv]

It's a little strange that journalctl needs --user but the logger command doesn't have a corresponding option

journalctl doesn't technically need --user, but there seems no point in retrieving other uids' log messages even if we have permission to do so (in Debian that would mean membership in the systemd-journal or adm group, other distros will vary).

logger doesn't need a --user option, because what other uid would I be writing to the log as, if not my own?