tests: add "shellcheck" tests for "ksh" scripts

.travis.yml

@@ -2,7 +2,7 @@
 dist: trusty
 install:
   - sudo apt-get update
-  - sudo apt-get --no-install-recommends install devscripts python python3 ruby php5-cli gawk ksh zsh pylint
+  - sudo apt-get --no-install-recommends install devscripts python python3 ruby php5-cli gawk ksh zsh pylint shellcheck
   - sudo apt-get --no-install-recommends install pkg-config libdb-dev libvirt-dev libexpat-dev
   # - Munin/Plugin.pm is in "munin-node" on precise
   - sudo apt-get --no-install-recommends install munin-node

t/test.t

@@ -85,12 +85,20 @@ sub process_file {
         };
     }
     elsif ( $interpreter =~ m{/bin/ksh} ) {
+        subtest $filename => sub {
+            plan tests => 2;
             run_check(
                 {   command     => [ 'ksh', '-n', $file ],
                     description => 'ksh syntax check',
                     filename    => $filename
                 }
             );
+            run_check(
+                {   command     => [ 'shellcheck', $file ],
+                    description => 'shellcheck'
+                }
+            );
+        }
     }
     elsif ( $interpreter =~ m{bash} ) {
         run_check(