Bump EPEL release rpm for RHEL 7 to 7.0-2

Change-Id: I67aca97770cd6f89072e881ae37e39d70bfaba53
retry apt operations to avoid network issues

One of the major gate failures is do to something being wrong with
the apt mirrors. The Acquire group provides an implicit retry on
network operations which seems like it might be helpful here.

Ref: http://linux.die.net/man/5/apt.conf

Change-Id: I099f47ed86ad6a3d4296bff4cce75e7f7d946d27
Related-Bug: #1286635
Support multiple Cinder backend types

This is the first step in supporting multiple Cinder backend types at
once.  It initially converts the existing hard-coded multi-lvm support
to a new cinder_backends driver form.  Eventually the cinder_plugins
will be converted to this form so they can be enabled more than just
one at a time.

The default configuration should be identical to the previous defaults,
including for both True and False values of CINDER_MULTI_LVM_BACKEND.

The existing cinder_plugins are expected to be removed when this is
complete. They should continue to work until they have been converted.

Change-Id: I93b8ef32832269d730c76a6dc24ddb4f20c6d9df
Handle failure of openstack endpoint

Change 4f7bf6963a1e9ae03bc0ae9189874cba561ad62f introduced finding the
endpoint via "openstack endpoint show" only.  Previously that output
was piped through grep, etc. so it handled fell back to a blank
output when the endpoints were not available.

Ignore failures of this command so the blank output is matched

Change-Id: Iae2f09784ffa38efd2f858513bf284c84c32edac
Add an environment variable to enable extensions in keystone

Following https://review.openstack.org/#/c/44401/3

Change-Id: I8e0391cd68e29e6d57c0f35517bf4155110861c7
Closes-Bug: #1218733
Co-Authored-By: Yong Sheng Gong <gongysh@unitedstack.com>
Use curl to download from github.com

Github recently removed some sslv3 ciphers - wget seems to only
enable a subset of the ciphers available so fails now, but curl
continues to succeed.

Use --no-sessionid to work around
https://bugzilla.redhat.com/show_bug.cgi?id=1098711

Change-Id: Ia110bd2d0a222e438189c10a9c1a236bd7ea3d0e
XenAPI: Tail output from stack.sh

While installing devstack in XenServer's DomU we can easily
track the output so end-users have much more visibility of
both what is going on and what (if anything!) went wrong.

Change-Id: I7d12a13cea9dffda6c1388ce711b6adf76cae72c
Merge "retry apt operations to avoid network issues"
Merge "Use curl to download from github.com"
Merge "Handle failure of openstack endpoint"
Merge "Add an environment variable to enable extensions in keystone"
Merge "XenAPI: Tail output from stack.sh"
Merge "Bump EPEL release rpm for RHEL 7 to 7.0-2"
Merge branch 'cinder-backends' into dt-test
Merge branch 'test-ini-improvements' into dt-test
Merge branch 'usb-prereq' into dt-test
Merge branch 'conf-tempest' into dt-test