Currently the ec2 collector polls the nova metadata service every
$polling_period even though the data is not expected to change and no
known config actions have been written to respond to changes in these
values.
With larger overclouds, this metadata polling will cause noticeable
load on the undercloud, especially nova-api and neutron (for port
lookups).
This change will check for data in /var/lib/os-collect-config/ec2.json
and simply return that if it exists.
Change-Id: I84156f8b005b319fccf8ac17af8943aefb0a8f6d
Closes-Bug: #1619072
a950edb320