Atomic_scan: add option to override fetching of new CVE data

[baude]

* The openscap-daemon can now optionally take a switch
  to override the behavior defined in its configuration
  file as to whether to fetch new CVE input data or
  not.

    --fetch_cves is now a bool (True|False) where true
        means to pull new, false means do not attempt
        to pull aka "phone home"

* Added timeout value of 99999 to override the default dbus
  connection timeout of 25 seconds.  This allows longer
  scans to complete and not throw an Exception.

* Added a small def to detect a bool value based on True,
  true, yes, y, 1 and so on

[baude]

Replaces #184 and squashed into one commit.

[rhatdan]

@baude You did not need to close the old, you could have merged the two together and then done a --force push.

[rhatdan]

LGTM