fix: make create_instance work with command line

[skuruppu]

Checklist

• [ ] Tests pass
• [ ] Lint pass: bundle exec rubocop
• [x] Please merge this PR for me once it is approved.

[skuruppu]

@dazuma it seems that the test failures are unrelated to this PR. The "Ruby Newest" and "Ruby Oldest" checks are stuck but I don't think these are Kokoro jobs so I don't know how to trigger them again.

[hengfengli]

@dazuma Gentle ping.

[skuruppu]

There is a failure in "Ruby Newest" related to Spanner, which is:

Failure/Error:
  write_read_bool_array project_id: @project_id,
                        instance_id: @instance.instance_id,
                        database_id: database.database_id

ArgumentError:
  wrong number of arguments (given 1, expected 2)
./spanner_samples.rb:1506:in `write_read_bool_array'
./spec/spanner_samples_spec.rb:1456:in `block (3 levels) in <top (required)>'
./spec/spanner_samples_spec.rb:128:in `capture'
./spec/spanner_samples_spec.rb:1455:in `block (2 levels) in <top (required)>'

But we didn't touch this code in this PR. I stared at the lines specified in the stack trace and I couldn't find an issue. Also the same test passes in Ruby 2.7 which is the only version of Ruby the Spanner tests are actually run against.

@dazuma what is the version used by "Ruby Newest"?

[bajajneha27]

@skuruppu Ruby-oldest is failing because of rubocop change, that can be fixed. Ruby-newest is failing with timeout; may be we can try running that in the main branch and see, to be sure.