Make the VMware datastore backend more robust

[Arnaud Legendre]

Several issues to address:

- need better error handling for the add,get,get_size,delete operations: need to catch exception when httplib call fails, also need to log when the response is not expected.
- need to handle cases where the store_image_dir contains non expected characters. It should support the following use cases:
/openstack_glance
openstack_glance
openstack_glance/
openstack glance -> this one should fail with logging
openstack+glance
etc.
- need to quote special characters

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/80098

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/80098
Committed: https://git.openstack.org/cgit/openstack/glance/commit/?id=551cad4c7bf7043c8942319fc46e58d851051b2c
Submitter: Jenkins
Branch: master

commit 551cad4c7bf7043c8942319fc46e58d851051b2c
Author: Arnaud Legendre <email address hidden>
Date: Wed Mar 12 15:18:48 2014 -0700

    Make the VMware datastore backend more robust

    This patch contains several fixes related to invalid configurations
    and corner cases:
    - better error handling for the store operations
    - better logging when response is not successful
    - better support for various store_image_dir formats

    Change-Id: I6c0003e29d621c1f71490cb9fce163dc840a113f
    Closes-Bug: #1291646