Catching exception on initial ReadState action

The `ReadState` action gets called within the `IsCreated` action (through the use of the `env[:machine].state` attribute).  Since the libvirt domain isn't created yet when the initial `IsCreated` check happens, it is throwing an exception (`Libvirt::RetrieveError`).  The existing code is just checking for a `nil` result instead of an exception.

```
An error occurred while executing multiple actions in parallel.
Any errors that occurred are shown below.

An unexpected error ocurred when executing the action on the
'default' machine. Please report this as a bug:

Call to virDomainLookupByUUID failed: Domain not found: no domain with matching uuid '1c62cff9-d165-4bfe-92d1-a1855e0bb146'

/home/benkeith/.vagrant.d/gems/gems/fog-1.19.0/lib/fog/libvirt/requests/compute/list_domains.rb:9:in `lookup_domain_by_uuid'
/home/benkeith/.vagrant.d/gems/gems/fog-1.19.0/lib/fog/libvirt/requests/compute/list_domains.rb:9:in `list_domains'
/home/benkeith/.vagrant.d/gems/gems/fog-1.19.0/lib/fog/libvirt/models/compute/servers.rb:17:in `get'
/home/benkeith/.vagrant.d/gems/gems/vagrant-libvirt-0.0.14/lib/vagrant-libvirt/action/read_state.rb:24:in `read_state'
/home/benkeith/.vagrant.d/gems/gems/vagrant-libvirt-0.0.14/lib/vagrant-libvirt/action/read_state.rb:15:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/warden.rb:34:in `call'
/home/benkeith/.vagrant.d/gems/gems/vagrant-libvirt-0.0.14/lib/vagrant-libvirt/action/connect_libvirt.rb:19:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/warden.rb:34:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/builtin/config_validate.rb:25:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/warden.rb:34:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/builder.rb:116:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/runner.rb:69:in `block in run'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/util/busy.rb:19:in `busy'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/runner.rb:69:in `run'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/machine.rb:147:in `action'
/share/code/vagrant/vagrant-libvirt/lib/vagrant-libvirt/provider.rb:58:in `state'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/machine.rb:321:in `state'
/home/benkeith/.vagrant.d/gems/gems/vagrant-libvirt-0.0.14/lib/vagrant-libvirt/action/is_created.rb:12:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/warden.rb:34:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/builder.rb:116:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/runner.rb:69:in `block in run'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/util/busy.rb:19:in `busy'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/runner.rb:69:in `run'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/builtin/call.rb:43:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/warden.rb:34:in `call'
/home/benkeith/.vagrant.d/gems/gems/vagrant-libvirt-0.0.14/lib/vagrant-libvirt/action/connect_libvirt.rb:84:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/warden.rb:34:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/builtin/config_validate.rb:25:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/warden.rb:34:in `call'
/home/benkeith/.vagrant.d/gems/gems/vagrant-berkshelf-1.3.7/lib/berkshelf/vagrant/action/configure_chef.rb:23:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/warden.rb:34:in `call'
/home/benkeith/.vagrant.d/gems/gems/vagrant-berkshelf-1.3.7/lib/berkshelf/vagrant/action/load_shelf.rb:28:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/warden.rb:34:in `call'
/home/benkeith/.vagrant.d/gems/gems/vagrant-berkshelf-1.3.7/lib/berkshelf/vagrant/action/set_ui.rb:12:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/warden.rb:34:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/builtin/env_set.rb:19:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/warden.rb:34:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/builder.rb:116:in `call'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/runner.rb:69:in `block in run'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/util/busy.rb:19:in `busy'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/action/runner.rb:69:in `run'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/machine.rb:147:in `action'
/opt/vagrant/embedded/gems/gems/vagrant-1.4.3/lib/vagrant/batch_action.rb:63:in `block (2 levels) in run'
/home/benkeith/.vagrant.d/gems/gems/logging-1.8.1/lib/logging/diagnostic_context.rb:323:in `call'
/home/benkeith/.vagrant.d/gems/gems/logging-1.8.1/lib/logging/diagnostic_context.rb:323:in `block in create_with_logging_context'
```