Merge lp://qastaging/~afrantzis/lightdm/logrotate into lp://qastaging/lightdm

I don't like the logic in is_log_file_managed_by_logrotate() - as well as having the log directory hard-coded this is inferring behaviour about how Ubuntu has configured LightDM.

Instead, I think open_log_file() should have a flag to say if the existing file should be backed up. For the system logs (i.e. in /var/log/lightdm, the main log, the X logs, the greeter logs etc) don't do the backup. For the other logs (session log) - do the backup.

Ideally we'd actually have a configuration item to disable log backups but it's not essential and can be added later if necessary.

Also please change the new logging code to match existing style: open_log_file() -> log_file_open()

Thanks!

FAILED: Continuous integration, rev:2209
http://jenkins.qa.ubuntu.com/job/lightdm-ci/313/
Executed test runs:
    FAILURE: http://jenkins.qa.ubuntu.com/job/lightdm-wily-amd64-ci/3/console
    FAILURE: http://jenkins.qa.ubuntu.com/job/lightdm-wily-armhf-ci/3/console

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> Instead, I think open_log_file() should have a flag to say if the existing
> file should be backed up. For the system logs (i.e. in /var/log/lightdm, the
> main log, the X logs, the greeter logs etc) don't do the backup. For the other
> logs (session log) - do the backup.

OK. Let me know if the following plan sounds good:

1. process_set_log_file() and session_set_log_file() will get a flag about whether to perform a backup or not, or alternatively we can add *_set_log_file_backup(..., gboolean backup)
2. Session will perform a backup by default (since their default log file is .xsession-errors)
3. At all invocations of *_set_log_file() in the current code the flag will be set to FALSE (don't backup), since all of them are considered system logs (in the current code session logs use the default log value of Session)

> Ideally we'd actually have a configuration item to disable log backups but
> it's not essential and can be added later if necessary.
>
> Also please change the new logging code to match existing style:
> open_log_file() -> log_file_open()

Ack.

Sounds good!