[JUJU-3364] Fix manual aws

[jack-w-shaw]

Previously we would branch on if a vpc has been created. If one already exists, validate it is correctly configured or fail. However, somehow the vpc ends up incorrectly configured. Specifically the subnet disappears

So instead perform each step in setting up the vpc idempotently

Checklist

• Code style: imports ordered, good names, simple structure, etc
• Comments saying why design decisions were made
• [ ] Go unit tests, with comments saying what you're testing
• Integration tests, with comments saying what you're testing
• [ ] doc.go added or updated in changed packages

QA steps

Base cases

With a 'clean' aws state (i.e. no vpcs called 'manual-deploy')

Ensure the following succeeds

./main.sh -v -c aws -p aws -R eu-west-2 manual test_deploy_manual

This should contain output:

===> Creating vpc vpc-0987e5dd6fee2d87b
===> Creating igw igw-036ecbd393d8fae51
===> Creating subnet subnet-030d0e55ee07d3870
===> Creating secgroup sg-057e2e3611589c4f6
===> Creating machines in aws

Now that resources have been created, run the suite again

./main.sh -v -c aws -p aws -R eu-west-2 manual test_deploy_manual

This should contain output:

===> Re-using vpc vpc-0987e5dd6fee2d87b
===> Re-using igw igw-036ecbd393d8fae51
===> Re-using subnet subnet-030d0e55ee07d3870
===> Re-using secgroup sg-057e2e3611589c4f6
===> Creating machines in aws

Special cases

Manually delete (detach first) the internet gateway attached to the vpc and re-run the test suite. It should succees and contain:

===> Re-using vpc vpc-0987e5dd6fee2d87b
===> Creating igw igw-036ecbd393d8fae51
===> Re-using subnet subnet-030d0e55ee07d3870
===> Re-using secgroup sg-057e2e3611589c4f6
===> Creating machines in aws

Manually delete the subnet in out vpc and re-run the test suite. It should succees and contain:

===> Re-using vpc vpc-0987e5dd6fee2d87b
===> Re-using igw igw-036ecbd393d8fae51
===> Creating subnet subnet-030d0e55ee07d3870
===> Re-using secgroup sg-057e2e3611589c4f6
===> Creating machines in aws

Manually delete the sec group called ci-manual-deploy and re-run the test suite. It should succees and contain:

===> Re-using vpc vpc-0987e5dd6fee2d87b
===> Re-using igw igw-036ecbd393d8fae51
===> Re-using subnet subnet-030d0e55ee07d3870
===> Creating secgroup sg-057e2e3611589c4f6
===> Creating machines in aws

[hpidcock]

/merge