Add report subcommand, change scan subcommand options

[kotakanbe]

In the current implementation, Vuls scan and reporting at once.
If an error occurred while reporting, following reporting method will be ignored.
If you want to send a report again, you have to re-scan.

So, I'm planning to add report subcommand.
The scan subcommand always writes JSON files under results-dir.
The report subcommand reads JSON files, and then

• report via slack or Email, ...
• convert to various format(XML, text, ...)
• write to various places(AWS, S3, ...).

Options are shown below.

$ vuls scan -help
scan:
        scan
                [-config=/path/to/config.toml]
                [-results-dir=/path/to/results]
                [-cve-dictionary-dbpath=/path/to/cve.sqlite3]
                [-cve-dictionary-url=http://127.0.0.1:1323]
                [-cache-dbpath=/path/to/cache.db]
                [-ssh-external]
                [-containers-only]
                [-http-proxy=http://192.168.0.1:8080]
                [-ask-key-password]
                [-debug]
                [-debug-sql]
                [SERVER]...

$ vuls report -help
report:
        report
                [-to-email]
                [-to-slack]
                [-to-azure-blob]
                [-to-s3]
                [-to-localfile]
                [-to-stdout]
                [-format-xml]
                [-format-json]
                [-format-html]
                [-format-csv]
                [-format-one-line-text]
                [-format-short-text]
                [-format-full-text]
                [-gzip]
                [-lang=en|ja]
                [-results-dir=/path/to/results]
                [-cvss-over=7]
                [-ignore-unscored-cves]
                [-http-proxy=http://192.168.0.1:8080]
                [-debug]
                [-aws-profile=default]
                [-aws-region=us-west-2]
                [-aws-s3-bucket=bucket_name]
                [-azure-account=accout]
                [-azure-key=key]
                [-azure-container=container]
                [SERVER]...

[jrw171819]

csv would be an interesting option for us