fix(alpine): support 3.12 (aquasecurity#517)

fix(app): add ArgsUsage (aquasecurity#508)

Add image subcommand (aquasecurity#493)

* config_test: Add missing assertions for TestNew

Signed-off-by: Simarpreet Singh <simar@linux.com>

* integration: Add integration tests for image subcommand.

Signed-off-by: Simarpreet Singh <simar@linux.com>

* refactor: bump up urfave/cli to v2.0

* refactor: apply DIY to image flags

* refactor: reorder sub commands

* feat: set hidden to global image options

* test(integration): insert --cache-dir before sub command

* README: update readme to reflect new usage

Signed-off-by: Simarpreet Singh <simar@linux.com>

* chore(README): add image subcommand

* fix(flags): define aliases according to urfave/cli v2.0 style

Co-authored-by: knqyf263 <knqyf263@gmail.com>

chore(ci): move integration tests to GitHub Actions (aquasecurity#485)

* fix(standalone): add defer to close databases

* test(client/server): launch a server only once

* test(docker_engine): remove the duplicated case

* test(docker_engine): copy a database only once

* test(standalone): copy a database only once

* test(server): fix tests according to updated mock

* chore(mod): update

* chore(ci): add integration tests to GitHub Actions

* chore(ci): bump up Go to 1.14

* chore(ci): remove integration tests from CircleCI

* chore(ci): add name

* chore(ci): add new lines

feat(db): store metadata as a file (aquasecurity#464)

* refactor: wrap errors

* feat(db): add the metadata file

* test(db): re-generate mocks

* fix(app): read metadata from the file in showVersion

* fix: open the database after downloading it

* fix(operation): use UpdateMetadata

* chore(mod): update dependency

* test(integration): fix tests

* fix(conf): rename TRIVY_NONSSL to TRIVY_NON_SSL

Fix CircleCI example in README.md (aquasecurity#451)

After trying to run trivy using CircleCI based on the sample configuration and failing, I want to suggest the following updates:

* `docker:18.09-git` no longer exists and causes workflow to fail, replaced with `stable-git` instead.
* added  `setup_remote_docker` or else the docker commands fail in the rest of the execution, as per https://circleci.com/docs/2.0/building-docker-images/#overview

Co-authored-by: Teppei Fukuda <knqyf263@gmail.com>

app: Fix a few edge cases with version flag (aquasecurity#443)

* app: Show just version if DB is missing

Signed-off-by: Simarpreet Singh <simar@linux.com>

* app: Dont panic if cache-dir is bogus

Signed-off-by: Simarpreet Singh <simar@linux.com>

* app: DRY up logic for showVersion

Signed-off-by: Simarpreet Singh <simar@linux.com>

fix(rpm): make it possible to scan non-RHEL images without rpm (aquas…

…ecurity#429)

fix(token): use the credential from enviroment variable (aquasecurity…

…#427)

chore(goreleaser): drop BSD support temporarily (aquasecurity#424)