Bug 1191602 - Docs: Clarify which commands should be run inside the VM

The shell prompts for each command example already mention vagrant, but
this can still be missed, so make the distinction extra clear.

docs/common_tasks.rst

@@ -17,7 +17,7 @@ In order to make the various services aware of a change in the code you need to
 Running the tests
 -----------------
 
-* You can run flake8 and the py.test suite using
+* You can run flake8 and the py.test suite inside the Vagrant instance, using
 
   .. code-block:: bash
 

docs/installation.rst

@@ -73,7 +73,7 @@ Setting up a local Treeherder instance
 Viewing the local server
 ------------------------
 
-* Start a gunicorn instance, to serve the static UI and API requests:
+* Start a gunicorn instance inside the Vagrant instance, to serve the static UI and API requests:
 
   .. code-block:: bash