Added PID namespace option

[a-canela]

The PID namespace Docker option was added to this Buildkite plugin. More details about this Docker option can be found here:

https://docs.docker.com/engine/reference/run/#pid-settings---pid

[jayco]

This looks good @a-canela!

It just needs a test, I couldn't seem to push a test commit onto your branch, so here's a passing test for this option :

diff --git a/tests/command.bats b/tests/command.bats
index 2f4d42e..63ffa30 100644
--- a/tests/command.bats
+++ b/tests/command.bats
@@ -225,6 +225,21 @@ setup() {
   unstub docker
 }

+@test "Runs BUILDKITE_COMMAND with pid namespace" {
+  export BUILDKITE_PLUGIN_DOCKER_PID=host
+  export BUILDKITE_COMMAND="echo hello world"
+
+  stub docker \
+    "run -it --rm --init --volume $PWD:/workdir --workdir /workdir --pid host --label com.buildkite.job-id=1-2-3-4 image:tag /bin/sh -e -c 'echo hello world' : echo ran command in docker"
+
+  run $PWD/hooks/command
+
+  assert_success
+  assert_output --partial "ran command in docker"
+
+  unstub docker
+}
+
 @test "Runs BUILDKITE_COMMAND with propagate environment" {
   export BUILDKITE_PLUGIN_DOCKER_PROPAGATE_ENVIRONMENT=true
   export BUILDKITE_PLUGIN_DOCKER_ENVIRONMENT_0=MY_TAG=value

If you could add it this in, I can merge and release this. Thanks again!

[a-canela]

@jayco test added! Sorry for the delay and thanks for your time :)

[pzeballos]

Hey @a-canela! Sorry for the very late reply! 😅 I'm reviewing your other PR #172 which contain also this functionality and it's more complete. I'll close this one. Thanks!