Allow override of os-brick library used by cinder

os-brick code was pulled out of cinder and made into its own library
https://review.openstack.org/#/c/155552/

added to requirements:
https://review.openstack.org/#/c/177372/

Integration tests were added
https://review.openstack.org/#/c/188156/

But they still use the version of os-brick from pip.

This change updates devstack to pull in the changes from
os-brick patch sets instead, when configured to do so.

Needed-by: Id2bc10782847861fe4bb5e9e46245654450e38fd

Change-Id: I5359dd37dfe94bd469d5ca35f9fbaeda61b5fac4
diff --git a/stackrc b/stackrc
index 09ba3e9..f8add4b 100644
--- a/stackrc
+++ b/stackrc
@@ -441,6 +441,10 @@
 GITREPO["ceilometermiddleware"]=${CEILOMETERMIDDLEWARE_REPO:-${GIT_BASE}/openstack/ceilometermiddleware.git}
 GITBRANCH["ceilometermiddleware"]=${CEILOMETERMIDDLEWARE_BRANCH:-master}
 
+# os-brick library to manage local volume attaches
+GITREPO["os-brick"]=${OS_BRICK_REPO:-${GIT_BASE}/openstack/os-brick.git}
+GITBRANCH["os-brick"]=${OS_BRICK_BRANCH:-master}
+
 
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