[release-1.22] Test sandwiched waypoint

[istio-testing]

Manual cherrypick required.

#973 failed to apply on top of branch "release-1.22":

Applying: Test sandwich waypoints
Using index info to reconstruct a base tree...
M	src/proxy/outbound.rs
M	src/test_helpers/linux.rs
M	src/test_helpers/tcp.rs
M	tests/namespaced.rs
Falling back to patching base and 3-way merge...
Auto-merging tests/namespaced.rs
CONFLICT (content): Merge conflict in tests/namespaced.rs
Auto-merging src/test_helpers/tcp.rs
Auto-merging src/test_helpers/linux.rs
CONFLICT (content): Merge conflict in src/test_helpers/linux.rs
Auto-merging src/proxy/outbound.rs
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 Test sandwich waypoints
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

[howardjohn]

#983