bosh-stemcell: rename RSpec context in cloudstack_spec.rb to match actual stage name

[coderabbitai]

Summary

In bosh-stemcell/spec/stemcells/cloudstack_spec.rb, the RSpec context string "installed by bosh_disable_password_authentication" does not match the actual implementation location (stemcell_builder/stages/base_ssh/apply.sh). This mismatch can cause confusion when running specs or debugging failures.

Suggested change

-  context "installed by bosh_disable_password_authentication" do
+  context "installed by base_ssh" do

References

• Identified in PR bosh-stemcell: introduce Gemfile, move deps to gemspec #543: bosh-stemcell: introduce Gemfile, move deps to gemspec #543
• Review comment: bosh-stemcell: introduce Gemfile, move deps to gemspec #543 (comment)

Requested by @aramprice — deferred from PR #543 (adding standardrb) to be addressed separately.