chore: speedup pak command in tests

[tinygrasshopper]

added caching which can be turned on by setting an enviornment variable on local
to speedup your local dev loops while running pak

[#181404983]

Signed-off-by: James Norman normanja@vmware.com

Checklist:

• Have you added Draft Release Notes in docs/draft-release-notes.md?
• Have you followed the Conventional Commits specification?

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/181523489

The labels on this github issue will be updated when the story is started.

[blgm]

• Should there be changes to the Makefile to set the variable?
• Does it make sense to expose this as a feature for brokerpak developers. Should there be a $HOME/.pakcache directory created as a default, to speed up the development process?

[tinygrasshopper]

• Should there be changes to the Makefile to set the variable?

Makes sense, added a new task to run integration tests cached. We dont want to change the default ci/flow to this one

• Does it make sense to expose this as a feature for brokerpak developers. Should there be a $HOME/.pakcache directory created as a default, to speed up the development process?

Makes sense, added $PWD/.pak-cache instead