Use virtualenv Python for stub connections to workaround problem

../data/stubs/stub-kubectl.py exec -it localhost -- /usr/bin/python -c "...":

    Traceback (most recent call last):
      File "<string>", line 1, in <module>
    LookupError: unknown encoding: base64

It's not clear why this is happening. "stub-kubectl.py" is executed with
the 2.7 virtualenv, while the exec() that happens inside stub-kubectl
was for "/usr/bin/python".

That second Python can't find chunks of its stdlib:

    stat("/usr/lib/python2.7/encodings/base64", 0x7ffde8744c60) = -1 ENOENT (No such file or directory)
    open("/usr/lib/python2.7/encodings/base64.so", O_RDONLY) = -1 ENOENT (No such file or directory)
    open("/usr/lib/python2.7/encodings/base64module.so", O_RDONLY) = -1 ENOENT (No such file or directory)
    open("/usr/lib/python2.7/encodings/base64.py", O_RDONLY) = -1 ENOENT (No such file or directory)
    open("/usr/lib/python2.7/encodings/base64.pyc", O_RDONLY) = -1 ENOENT (No such file or directory)
    write(2, "Traceback (most recent call last):\n", 35) = 35
    write(2, "  File \"<string>\", line 1, in <module>\n", 39) = 39

tests/ansible/integration/stub_connections/kubectl.yml

@@ -13,6 +13,7 @@
   - custom_python_detect_environment:
     vars:
       ansible_connection: kubectl
+      ansible_python_interpreter: python  # avoid Travis virtualenv breakage
       mitogen_kubectl_path: stub-kubectl.py
     register: out
 

tests/ansible/integration/stub_connections/lxc.yml

@@ -10,6 +10,7 @@
   - custom_python_detect_environment:
     vars:
       ansible_connection: lxc
+      ansible_python_interpreter: python  # avoid Travis virtualenv breakage
       mitogen_lxc_attach_path: stub-lxc-attach.py
     register: out
 

tests/ansible/integration/stub_connections/lxd.yml

@@ -10,6 +10,7 @@
   - custom_python_detect_environment:
     vars:
       ansible_connection: lxd
+      ansible_python_interpreter: python  # avoid Travis virtualenv breakage
       mitogen_lxc_path: stub-lxc.py
     register: out
 

tests/ansible/integration/stub_connections/mitogen_doas.yml

@@ -10,6 +10,7 @@
   - custom_python_detect_environment:
     vars:
       ansible_connection: mitogen_doas
+      ansible_python_interpreter: python  # avoid Travis virtualenv breakage
       ansible_doas_exe: stub-doas.py
       ansible_user: someuser
     register: out

tests/ansible/integration/stub_connections/mitogen_sudo.yml

@@ -10,6 +10,7 @@
   - custom_python_detect_environment:
     vars:
       ansible_connection: mitogen_sudo
+      ansible_python_interpreter: python  # avoid Travis virtualenv breakage
       ansible_user: root
       ansible_become_exe: stub-sudo.py
       ansible_become_flags: -H --type=sometype --role=somerole

tests/ansible/integration/stub_connections/setns_lxc.yml

@@ -18,6 +18,7 @@
         -i localhost,
         -c setns
         -e mitogen_kind=lxc
+        -e ansible_python_interpreter=python
         -e mitogen_lxc_info_path={{git_basedir}}/tests/data/stubs/stub-lxc-info.py
         -m shell
         -a "echo hi"

tests/ansible/integration/stub_connections/setns_lxd.yml

@@ -18,6 +18,7 @@
         -i localhost,
         -c setns
         -e mitogen_kind=lxd
+        -e ansible_python_interpreter=python
         -e mitogen_lxc_path={{git_basedir}}/tests/data/stubs/stub-lxc.py
         -m shell
         -a "echo hi"