Install shellcheck if needed

src/freedombone-tests

@@ -66,6 +66,10 @@ function test_app_function_type {
 }
 
 function test_static_analysis {
+    if [ ! -f /usr/bin/shellcheck ]; then
+        apt-get -yq install shellcheck
+    fi
+
     FILES="/usr/share/${PROJECT_NAME}/apps/${PROJECT_NAME}-*"
 
     for filename in $FILES