Bug 16974: Make koha-plack should check and fix log files permissions

Bug 16974: Make koha-plack should check and fix log files permissions

This patch adds a function to the koha-plack script so it checks for log file
existence and its permissions. This function is called from the start_plack function.

If some of this conditions are not fulfilled, it solves the situation by either
touching and/or changing the permissions accordingly for the instances' plack log files.

To test:
- Run (on kohadevbox):
  $ cd kohaclone
  $ debian/scripts/koha-plack --start kohadev
  $ debian/scripts/koha-plack --stop  kohadev
  $ ls /var/log/koha/kohadev/plack*
- Verify ownership of the created files (they might belong to the root user)
- Apply the patch
- Run:
  $ chown root:root /var/log/koha/kohadev/plack*
  $ debian/scripts/koha-plack --start kohadev
  $ ls /var/log/koha/kohadev/plack*
=> SUCCESS: Files belong to kohadev-koha:kohadev-koha
- Run:
  $ debian/scripts/koha-plack --stop  kohadev
  $ rm /var/log/koha/kohadev/plack*
  $ debian/scripts/koha-plack --start kohadev
  $ ls /var/log/koha/kohadev/plack*
=> SUCCESS: Files are created and belong to kohadev-koha:kohadev-koha
- Sign off :-D

Signed-off-by: Mirko Tietgen <mirko@abunchofthings.net>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>