Add hooks & define active/offline as running/not

Hosts entries shouldn't only be added/removed upon creation/destruction.
The persistence of /etc/hosts entries while a vm is in a halted or
suspended state is undesirable especially when hostmanager.manage_host
is set to true. That would mean your host's /etc/hosts would retain
entries even if you aren't currently using a vm.  The vm would have to
be destroyed for the entry to be removed from the host's /etc/hosts.

Adding hooks for halt, resume and suspend commands and changing the
concept of active and offline states from created or not_created to
running or not running allows a vm's entry to be added when it is put
in a running state and removed when it is not running.

The hostmanager.include_offline can be set to true if one still desires
to have not_created or not running machines' entries included in the
/etc/hosts file.
Merge pull request #34 from jeremiahsnapp/define_active_as_running

Add hooks & define active/offline as running/not