(#605) Populate the PT__installdir environment variable

When Bolt run a task, _installdir is set to the directory where the task
files have been copied.  In our case, we build a simiar hierarchy in the
file directory under the task spool directory, so set this environment
variable accordingly.

https://puppet.com/docs/bolt/latest/writing_tasks.html#sharing-task-code

lib/mcollective/util/tasks_support.rb

@@ -186,6 +186,8 @@ def task_environment(task, task_id, task_caller)
           environment["PT_%s" % k] = v.to_s
         end
 
+        environment["PT__installdir"] = File.join(request_spooldir(task_id), "files")
+
         environment
       end
 

spec/unit/mcollective/util/tasks_support_spec.rb

@@ -387,9 +387,11 @@ module Util
       describe "#task_environment" do
         it "should set the environment for both or environment methods" do
           ["both", "environment"].each do |method|
+            ts.stubs(:request_spooldir).returns(File.join(cache, "test_1"))
             task_run_request_fixture["input_method"] = method
             task_run_request_fixture["input"] = '{"directory": "/tmp", "bool":true}'
             expect(ts.task_environment(task_run_request_fixture, "test_id", "caller=spec.mcollective")).to eq(
+              "PT__installdir" => File.join(cache, "test_1", "files"),
               "PT_directory" => "/tmp",
               "PT_bool" => "true",
               "_task" => "choria::ls",