Bug 13793: Make the installer output the result of the updates under Plack

Bug 13793: Make the installer output the result of the updates under Plack

Test plan:
0/ Start plack for intranet
1/ Create a new entry in updatedatabase.pl, something like:

$DBversion = "3.19.00.013";
if(CheckVersion($DBversion)) {
    print "Upgrade to $DBversion done (Bug test plack - This is a
est)\n";
    print "Upgrade to $DBversion done (Bug test plack - This is anoter
est)\n";
    print "Upgrade to $DBversion done (Bug test plack - This is a third
est)\n";
    warn "this is an error";
}
and modify the kohaversion.pl accordingly.
You can also warn something to simulate an error.
2/ Go on the mainpage (or wherever you want), you should be redirected
to the installer
3/ Notice that the output of the updatedatabase is displayed on the
screen.
4/ Confirm that new files have been created in your Koha log directory
(check the logdir entry in your koha conf file).
5/ Confirm that the output is still displayed without Plack.

Signed-off-by: Dobrica Pavlinusic <dpavlin@rot13.org>
Signed-off-by: Brendan Gallagher <brendan@bywatersolutions.com>
Signed-off-by: Brendan Gallagher <brendan@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>