Changes

testenv: set args.podman = False if action != "run"

Fix "./testenv.py clean":

    File "/home/user/code/osmo-dev/src/osmo-ttcn3-hacks/_testenv/testenv/cmd.py", line 85, in run
      if not no_podman and testenv.args.podman:
                           ^^^^^^^^^^^^^^^^^^^
  AttributeError: 'Namespace' object has no attribute 'podman'

Change-Id: I44d5229aa481bfed13c006368d590e1486536c0e

testenv: cmd: pass all env vars without --podman

As suggested by Pau, pass all environment variables to through testenv
if it is running without podman. This way a custom TTCN3_DIR,
TTCN3_BIN_DIR and more variables that may make sense when running
directly on the host, work as expected.

Closes: OS#6544
Change-Id: I5e710a1ee7185a3f6f4f1e98f201f3f6fda2be55

S1AP_Emulation: Fix new_ctx never set when building security header

The flag was never set to true. It needs to be set to true when building
the security head of Security Mode Complete after receiving Security
Mode Command with a new EPS security context.
TS 24.301 5.4.3.3

Change-Id: I76ad46f7ee5f49698e41da729cb6422866202951

S1AP_Emulation: Fix building security headers for Integrity and Ciphering

The fact that the network instructs the UE to use EEA0 encryption (null
algo) doesn't mean the UE should mark the NAS frames in the security
header as non-ciphered. They need to be marked as IP+ciphered in the
outer header, and as plain in the inner one.

Now TTCN3 behaves like a UE recorded while executing a similar test
case. Moreover, wireshark is now happy decoding the messages.

Change-Id: Ifd4fe83e7b5aefdaafe7ce1c8b1ec6a67c65819c

testenv/README: update

Point at ./testenv.py -h and describe that everything runs in 1
container with --podman.

Change-Id: Ie9eee8cf14ba2069c1cd5bd6ab703f3f6ccdc100