OVERCLOUD_IP and OVERCLOUD_ENDPOINT from heat outputs

Read OVERCLOUD_ENDPOINT from heat with command:
heat output-show $STACKNAME KeystoneURL

OVERCLOUD_IP is parsed from that url unless NeutronPublicInterfaceIP
variable is set.

This change is required for:
- keystone endpoints point out to vip address
- prevents devtest_overcloud.sh from failing when OVERCLOUD_CONTROLSCALE > 1

Change-Id: I6c3c8c893d52c76519805941ee21759a1fc69ca1
Merge "OVERCLOUD_IP and OVERCLOUD_ENDPOINT from heat outputs"