allow some failures in esx_portgroup resources

Connection errors can occur while modifying properties of the
management network resource. This change logs those errors rather than
failing the whole run.
allow esx resources to work without vcenter

Many esx resources searched for the esx host to configure under a
specific datacenter. This prevents the esx host itself from being used
as the transport because the host does not exist in a datacenter.

This patch falls back to searching for the host by ip or dns name
alone if no path is specified for the host.
Merge pull request #43 from gavin-scott/managment-network-disconnect

allow some failures in esx_portgroup resources
Merge pull request #42 from gavin-scott/configure-esxi

allow esx resources to work without vcenter