Give instance default hostname if hostname is empty

[OpenStack Infra]

https://review.openstack.org/227176
commit db45b1eca8a3db8f1b5153c58b138711ed69c388
Author: Eli Qiao <email address hidden>
Date: Thu Sep 17 13:57:24 2015 +0800

    Give instance default hostname if hostname is empty

    Instance hostname is generated by displayname, currently, displayname
    can be '----', and other Non-ASCII character such as Chinese characters,
    sanitize_hostname will return empty in such cases.

    This patch adds a helper function _default_host_name to give an instance
    default name if sanitize_hostname returns empty hostname. And,
    sanitize_hostname will truncated to 63 if the host name is too long.

    Also Window, Linux, and Dnsmasq have different limitation:

    Windows: 255 (net_bios limit to 15, but window will truncate it)
    Linux: 64
    Dnsmasq: 63

    Due to nova-network will leverage dnsmasq to set hostname, so we chose
    63.

    Besides, added more test cases to cover sanitize_hostname.

    DocImpact
    Closes-Bug: #1495388
    Co-authored-by: Alex Xu <email address hidden>

    (cherry picked from commit bc6f30de953303604625e84ad2345cfb595170d2)

    Conflicts:
     nova/tests/unit/compute/test_compute_api.py
     nova/tests/unit/test_utils.py
     nova/utils.py

    Change-Id: I443b51e0576cf657d96e498d6700bfc34d987301

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/336965

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/336965
Committed: https://git.openstack.org/cgit/openstack/openstack-manuals/commit/?id=9b96fbcd4956059af0dc4e6dd426219f311f6778
Submitter: Jenkins
Branch: master

commit 9b96fbcd4956059af0dc4e6dd426219f311f6778
Author: KATO Tomoyuki <email address hidden>
Date: Mon Jul 4 10:53:14 2016 +0900

    [user-guide] add note about hostname 63 chars limitation

    Change-Id: Ic8618ba864d8341d4d4df103c8cd33f10ce64b27
    Closes-Bug: #1504213

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/openstack-manuals 15.0.0 release.