WIP: Dont swallow errors from populateiamdata

[patrobinson]

This PR creates a failing test to exhibit behaviour found in #57.
When an invalid policy document is returned (either because its' incorrect from AWS or we've not decoded it correctly) that error is swallowed and not shown to the user. Instead the policy and any other policies are not synced from AWS and we get a diff that tries to push them all back up.

Test output:

Running tool: /usr/local/bin/go test -timeout 30s -run ^(TestFetchIamData)$

2019/03/05 11:58:39 Error Fetching IAM Data invalid URL escape "%zz"
--- FAIL: TestFetchIamData (0.00s)
    /Users/patrickrobinson/src/iamy/iamy/aws_test.go:102: We expected fetch IAM to fail because the policy document was invalid. But it didn't
FAIL
exit status 1
FAIL	_/Users/patrickrobinson/src/iamy/iamy	0.014s
Error: Tests failed.