relax tenant subnet validation to allow it to be shared

This commit removes the "must be on a dedicated subnet" check for tenant
network. However, sharing is only supported for Neutron vxlan and gre.
For Neutron vlan and flat, or for Nova networking, the tenant network
type must still be separated from the rest.
Merge pull request #367 from sseago/relax-tenant-subnet-validation

relax tenant subnet validation to allow it to be shared
for discovery environment, ignore power management (bmc, etc)

We hit an issue where configuring fencing on the host pre-deployment caused
deploy reboot to fail. As it turns out, simply having the bmc nic's
username and password field filled in causes foreman to want to control
the host via bmc. This may be fine post-deployment (although we
probably have lingering bmc proxy problems for that to really work),
but for initial deployment, this breaks and I don't know that we
want to boot fencing-enabled hosts differently than others, even
if it does work -- so with this, discovery env hosts are rebooted
via the discovery image proxy regardless of whether they're
configured for fencing post-deployment
Merge pull request #369 from sseago/bmc-discovery-reboot

for discovery environment, ignore power management (bmc, etc)