To locate hdfs command in HDFS native driver

[weiting-chen]

Current HDFS native driver use "locate /bin/hdfs" to find the location for hdfs binary.
But this way could find an error path in different situation, it should be corrected and maybe doesn't need to find it out, just to call the command directly.
Let the user to configure the hdfs command to their default system.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/211147

[OpenStack Infra (hudson-openstack)]

Change abandoned by weiting-chen (<email address hidden>) on branch: master
Review: https://review.openstack.org/209825
Reason: Have already split it to two different patch for individual bugs.
So I will abandon it.
Please follow the other two patches.
https://review.openstack.org/#/c/211130/
https://review.openstack.org/#/c/211147/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/211147
Committed: https://git.openstack.org/cgit/openstack/manila/commit/?id=cf3ea378f07006daacb76c102170d519e58afcb6
Submitter: Jenkins
Branch: master

commit cf3ea378f07006daacb76c102170d519e58afcb6
Author: weiting-chen <email address hidden>
Date: Mon Aug 10 21:16:21 2015 +0800

    Fix bug to locate hdfs command in HDFS native driver

    No longer to locate hdfs command.
    Assume the ssh user has the authority to launch hdfs command.
    And the user must add hdfs in default PATH manually.

    Change-Id: Ia5d118a49ecea092848796067ae48dbead83c40e
    Closes-Bug: #1481568