Standardise pkExpect process execution with shell option

[emmacasolin]

Specification

Our pkExec and pkSpawn process execution utilities were standardised in MatrixAI/Polykey#436, however, pkExpect was left unchanged due to the lack of shell option for nexpect.spawn. nexpect.spawn always spawns a child process with the default shell: false, however, for this to work with our docker integration tests we need to be able to set the shell option to true. Doing this would require either forking nexpect or switching to a different library.

Additional context

• Standardise Process Execution in tests/utils/exec.ts Polykey#432 - Original issue for process execution standardisation with more detailed spec
• Standardise process execution for tests Polykey#436 - PR for standardising pkExec and pkSpawn (a similar procedure will be required to standardise pkExpect)

Tasks

1. Expose the shell option when calling nexpect.spawn or equivalent
2. Create pkExpectWithoutShell and pkExpectWithShell variants

[CMCDragonkai]

A quick PR upstream can also be done as it is unlikely to change many things.

Can you copy paste the code snippet relevant to be changed here.

[emmacasolin]

The shell option needs to be added to the context object: https://github.com/nodejitsu/nexpect/blob/master/lib/nexpect.js#L365-L376

And this needs to be passed through to spawn: https://github.com/nodejitsu/nexpect/blob/master/lib/nexpect.js#L257-L260

The type of the options here would also need shell to be added: https://github.com/nodejitsu/nexpect/blob/master/lib/nexpect.js#L344