inline_scan doesn't seem to honor -b correctly

[davidmankin]

Followup on #9

The problem

When I try to use the -b flag to point to a policy bundle I get an error that makes me think it doesn't understand the flag. (It tries to scan an image called policy_bundle.json)

Environment

OS X Mojave; bash script calling version 0.6.0 of inline_scan downloaded from github.

Details

When I try to use the -b flag to point to a policy bundle (either by relative path or absolute) I get the following error:

$ anchore-ci-tools/scripts/inline_scan scan -b ../anchore/policy_bundle.json -t 300 -p -r my.docker.registry/my-docker-image@sha256:211de8a383c...
...
time="2019-12-31T20:56:10Z" level=fatal msg="Error loading tar component manifest.json: archive/tar: invalid tar header"
	Ignoring invalid docker archive:  /anchore-engine/policy_bundle.json

Unable to activate policy bundle - /anchore-engine/policy_bundle.json -- using default policy bundle.
...
Error: Policy bundle null not found in DB
HTTP Code: 404
Detail: {'error_codes': []}
...

Actual Behaviour

Seems to run okay but with default policy bundle.

Expected Behaviour

How do you reproduce the error?

Surprisingly it seems somewhat flaky. It never seems to load the policy bundle but it does seem to vary whether it gives the "Error loading tar component" error.