improve metadata response time

[Andrey Pavlov]

metadata server sometimes too slow. cirros image can't recognize an answer if response time more than 10 sec:

2016-08-31 19:30:23.155 20792 DEBUG ec2api.metadata.api [req-d9218218-62cd-4688-972c-f9bb5a5fdd67 - - - - -] in: [u'2009-04-04', u'meta-data', u'instance-id'] get_metadata_item /home/apavlov/openstack/ec2-api/ec2api/metadata/api.py:110
2016-08-31 19:30:36.081 20792 DEBUG ec2api.metadata.api [req-d3c2b7fc-06d8-410c-8ff7-ae2e524221ef - - - - -] in: [u'2009-04-04', u'meta-data', u'instance-id'] get_metadata_item /home/apavlov/openstack/ec2-api/ec2api/metadata/api.py:110
2016-08-31 19:30:46.436 20792 DEBUG ec2api.metadata.api [req-d9218218-62cd-4688-972c-f9bb5a5fdd67 - - - - -] out: i-d11a11a6 get_metadata_item /home/apavlov/openstack/ec2-api/ec2api/metadata/api.py:133
2016-08-31 19:30:47.509 20792 DEBUG ec2api.metadata.api [req-d3c2b7fc-06d8-410c-8ff7-ae2e524221ef - - - - -] out: i-d11a11a6 get_metadata_item /home/apavlov/openstack/ec2-api/ec2api/metadata/api.py:133
2016-08-31 19:30:48.621 20792 DEBUG ec2api.metadata.api [req-a17fd02b-2163-4dcb-a55e-39aab31ff245 - - - - -] in: [u'2009-04-04', u'meta-data', u'instance-id'] get_metadata_item /home/apavlov/openstack/ec2-api/ec2api/metadata/api.py:110
2016-08-31 19:30:53.218 20792 DEBUG ec2api.metadata.api [req-a17fd02b-2163-4dcb-a55e-39aab31ff245 - - - - -] out: i-d11a11a6 get_metadata_item /home/apavlov/openstack/ec2-api/ec2api/metadata/api.py:133

[Andrey Pavlov (apavlov-e)]

fixed https://review.openstack.org/#/c/469075/