Change the way static config variable is set

Previously Ansible did not enable static interfaces configuration
correctly when 'static' was detected - new interfaces were still
generated and old configuration was diverted. Now it should correctly
define 'ifupdown_static_config' file so that rest of the role will not
muck around with /etc/network/interfaces by default.
Remove OpenVZ guest configuration

Currently 'debops.ifupdown' role detects static configuration and avoids
interface configuration automatically if 'static' configuration is
detected, which is the case on OpenVZ containers with venet interface
configuration. On the other hand, OpenVZ containers with veth interfaces
will benefit from automatic interface configuration when DHCP is
enabled.
Merge pull request #11 from drybjed/rewrite-static-check

Small updates to configuration autodetection