Retry getting the list of service plugins

On systems that start both neutron-server and neutron-l3-agent together,
there is a chance that the first call to neutron will timeout. Retry upto
4 more times to avoid the l3 agent exiting on startup.

This should make the l3 agent a little more robust on startup but still
not ideal, ideally it wouldn't exit and retry periodically.

Change-Id: I2171a164f3f77bccd89895d73c1c8d67f7190488
Closes-Bug: #1353953
Closes-Bug: #1368152
Closes-Bug: #1368795
Add admin tenant name to nova notifier

This change introduces the ability to use the nova admin
tenant name with the nova notifier in place of the nova
admin tenant id which may not be available when the neutron
service is being configured as is the case with tripleo
installations where the neutron service is configured and
started before the nova admin tenant has been configured in
keystone and thus does not have a known id.

DocImpact
Introduces the nova_admin_tenant_name configuration entry as
an optional configurable value in neutron.conf.  If the
nova_admin_tenant_name is configured and the nova_admin_tenanat_id
is not configured, a performance impact may be seen because
keystone will become involved in communication between neutron
and nova.

Change-Id: I33701d4dc9bf61595e44a49050c405ebca779091
Closes-Bug: #1331566
Merge "Retry getting the list of service plugins"
Merge "Add admin tenant name to nova notifier"