Check at least 2 l3 agents before trying to initialize neutron
Check at least 2 l3 agents before trying to initialize neutron

According to https://bugzilla.redhat.com/show_bug.cgi?id=1236578
it is reported that in a VM env the post deploy configuration of
Neutron fails with
  "ERROR: openstack Not enough l3 agents available to ensure HA

Implements a loop that retries 6 times to get at least 2 neutron
l3 agents before giving up, with 10 seconds sleep (idea is ~1 min).

Change-Id: Ic495da5bc84825581771c0724cc91a9b504100bf

rdo-management/python-rdomanager-oscplugin,openstack/python-tripleoclient