Beginnings of a docker plugin.

Scan for content of appropriate type, and identify the cert and key paths we
need to copy in for docker.
Docker plugin now copying certs and cleaning out old ones.

Unknown files should be left alone, CA certificates for one example.
Anything ending with .cert or .key however is fair game for removal.
Update spec and makefile for docker plugin.

Conflicts:
	subscription-manager.spec
Hook up docker plugin.
Hook up a configured hostname sub-dir for docker certs.
Rename to generic container content plugin.

Trademark issues.
Add container plugin update report.
Add a more thorough test.
Simplify container content plugin to it's own module.
Complete a test, and move to correct location.
Stylish updates.
Update spec and makefiles.
Case insensitive content type searching.
Test container content keypair equals method.
Assume /etc/docker/certs.d is owned by another package.
Copy cert/key mode to match their source files in /etc/pki/entitlement.
1119688: Improved error code usage in subman.

- Standardized most print & sys.exit calls with the system_exit
  abstraction.

- Standardized error code usage, using os.EX_* constants where appropriate:
  - EX_USAGE for improper usage of command options
  - EX_DATAERR for proper command usage with invalid provided data
  - EX_UNAVAILABLE for command options which are unsupported by the
    current server
  - EX_SOFTWARE for internal fatal errors
  - Others used somewhat liberally where seemingly appropriate

- Added error output to the status command:
  - 0 when the system is registered and no errors occur during the check
  - 1 when the system is not registered

- Updated the tests as necessary
Automatic commit of package [subscription-manager] release [1.13.6-1].
Support multiple container cert directories.

Due to redirects, docker will need to communicate with both a crane host, and
then the CDN.
Fix cert/key filenames for container plugin.

Base filename should match, so stop naming them SERIAL-key.key and instead just
SERIAL.key.