Bug 43159: Restore localisation of PERL5LIB and KOHA_HOME

This change localises PERL5LIB and KOHA_HOME,
which means that any changes made to PERL5LIB or KOHA_HOME
within _do_instance() in koha-plack are confined to the specific
instance being worked on in that function.

See Bugzilla for steps on how to reproduce the problem.

Test plan:
- Apply the patch
- sudo vi debian/scripts/koha-plack

Within _do_instance after PERL5LIB is set, add the following:
echo $PERL5LIB

- sudo koha-create --request-db test1
- sudo ./debian/scripts/koha-plack --restart test1 test1 test1 test1
- Note that now PERL5LIB stays constant:

/usr/share/koha/lib:/usr/share/koha/installer:/usr/share/koha/lib/installer

- git restore debian/scripts/koha-plack

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Laura_Escamilla <laura.escamilla@bywatersolutions.com>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>

debian/scripts/koha-plack

@@ -367,6 +367,12 @@ set_action()
 
 _do_instance() {
     local name=$1
+    #NOTE: It's very important that PERL5LIB and KOHA_HOME are local
+    #      By being local, we keep the PERL5LIB and KOHA_HOME specific
+    #      to the instance that we're working on right now.
+    #      If you disagree, please look at BZ 25778 and BZ 43159.
+    local PERL5LIB=$PERL5LIB
+    local KOHA_HOME=$KOHA_HOME
 
     adjust_paths_git_install $name
     PERL5LIB=$PERL5LIB:$KOHA_HOME/installer:$KOHA_HOME/lib/installer