Disable .pyc files for grenade multinode

Ironic's grenade multinode suffers from some of unique issues.

* Nova can never be upgraded as there is a static pin that increments
  higher. As such, newer nova can never run with older ironic.
* As Nova cannot be upgraded, it is left running throughout the test
  sequence.

The above two conditions result in possible breaking package upgrades
as the python environments are shared between the old and new
installations.

In order to better isolate the running processes, as would be in
most actual production environments, we need to minimize underlying
inter-reactions due to python library upgrades.

Credit goes to Jim Rollenhagen for coming up with this idea, once the
massive conundrum was fully explained. Thanks Jim!

Partial-Bug: #1744139
Change-Id: Ifdd119d9cdde2ead6c3e36862cc77da67d10f7d1

playbooks/legacy/grenade-dsvm-ironic-multinode-multitenant/run.yaml

@@ -15,6 +15,35 @@
         path: '{{ ansible_user_dir }}/workspace'
         state: directory
 
+    # NOTE(TheJulia): Python supports recompiling bytecode if a precompiled
+    # (.pyc) file is written to disk. Python will automatically recompile
+    # should that file disappear and attempt to load and use that bytecode.
+    # This can lead to unexpected and undesirable behavior such as python
+    # crashing.
+    #
+    # As this job scenario upgrades across possible structural changes to
+    # python modules, and operates in a mixed environment between releases
+    # it is a good idea to prevent scenarios where newer modules installed
+    # by packages are leveraged by un-upgraded services because their
+    # underlying python packages have been updated during runtime.
+    #
+    # This is unique to Ironic's rolling upgrade grenade job, as Nova is
+    # excluded from being upgraded in the stack, and Ironic is left in
+    # a half-upgraded situation. The net result of which is we have an
+    # unstable Nova installation.
+    # https://bugs.launchpad.net/ironic/+bug/1744139
+    #
+    # TODO(TheJulia): We either need to find a better way to test rolling
+    # upgrades. Something which supports virtualenvs would be ideal, as
+    # well as something that allows us greater upgrade order control as
+    # the Ironic upgrade sequence is problematic and breaks towards the end
+    # of every cycle.
+    - shell:
+        cmd: |
+          echo 'DefaultEnvironment="PYTHONDONTWRITEBYTECODE=1"' >>/etc/systemd/system.conf
+          systemctl daemon-reexec
+      become: yes
+
     - shell:
         cmd: |
           set -e