fix: execute commands using correct stack path

[katcipis]

Fixes: #14

Usually I like to add automated tests, but there isn't anything for the run function, and since we want to already refactor the design, it seems desireable to move run to be part of the core logic, not on cmd/main (like it was done with list/list changed).

Usually I would also refactor first + fix the bug on the new improved design, but since there is no tests the refactoring itself may break some features and we want a stable initial v0.0.1 ASAP.

So I did the unusual surgery mode fix. But refactoring around "run" should come ASAP.

[katcipis]

The current fix makes it more clear where commands will be run by using absolute paths, but it does introduce some inconsistency with how things are show on terrastack list, this modded version of the test script shows the difference:

#!/bin/bash

set -o errexit
set -o nounset

stack_absolute_path=$(mktemp -d)

cd "${stack_absolute_path}"

mkdir stack1
touch stack1/terrastack

mkdir stack2
touch stack2/terrastack

echo
echo "=== RUNNING INSIDE STACK BASE DIR ==="
# Running with absolute path basedir, inside stack, works:
terrastack run -b "${stack_absolute_path}" ls

echo "terrastack list"
terrastack list

echo
echo "=== RUNNING OUTSIDE STACK BASE DIR ==="
# Running with absolute path basedir, outside stack, breaks:
cd ..
terrastack run -b "${stack_absolute_path}" ls

echo "terrastack list"
terrastack list "${stack_absolute_path}"

Outputs:

=== RUNNING INSIDE STACK BASE DIR ===
Running on all stacks:
[/tmp/tmp.M0hXsYRJ3i/stack1] running /bin/ls
terrastack

[/tmp/tmp.M0hXsYRJ3i/stack2] running /bin/ls
terrastack

terrastack list
stack1
stack2

=== RUNNING OUTSIDE STACK BASE DIR ===
Running on all stacks:
[/tmp/tmp.M0hXsYRJ3i/stack1] running /bin/ls
terrastack

[/tmp/tmp.M0hXsYRJ3i/stack2] running /bin/ls
terrastack

terrastack list
tmp.M0hXsYRJ3i/stack1
tmp.M0hXsYRJ3i/stack2

Specially when running commands is involved, I kinda liked being able to see the absolute path + the code is easier to reason with (commands are run on a absolute path and that is it). But it does introduce an inconsistency with listing output.

For the v0.0.1 should we push with this or do further changes considering the PWD to replicate the list behavior ?

WDYT @mariux @i4ki ?

[i4ki]

I don't see this as an inconsistency because run needs to set its working directory to the stack directory, then if there's any permission error Go is going to report an absolute path in the error, and this will be very inconsistent.

So I vote to make the terrastack run show absolute paths but all list variants use relative by default.

[i4ki]

LGTM