Synchronize changes with perf testing

NCP-1564

* Adds a new index for quark_ip_addresses that helps with reallocation
* Removes the semaphore decorator from select_subnet

quark/db/migration/alembic/versions/29265c7bcd1f_.py

@@ -0,0 +1,26 @@
+"""empty message
+
+Revision ID: 29265c7bcd1f
+Revises: 4dbf83f37bc0
+Create Date: 2015-06-18 14:27:18.571918
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '29265c7bcd1f'
+down_revision = '4dbf83f37bc0'
+
+from alembic import op
+
+
+def upgrade():
+    op.create_index(op.f('ix_quark_reallocate_ip_addresses'),
+                    'quark_ip_addresses',
+                    ["network_id", "tenant_id", "version", "subnet_id",
+                     "deallocated_at"],
+                    unique=False)
+
+
+def downgrade():
+    op.drop_index(op.f('ix_quark_reallocate_ip_addresses'),
+                  table_name='quark_ip_addresses')

quark/db/migration/alembic/versions/HEAD

@@ -1 +1 @@
-4dbf83f37bc0
+29265c7bcd1f

quark/ipam.py

@@ -816,10 +816,6 @@ class QuarkIpam(object):
                 return False
         return True
 
-    # RM6180(roaet):
-    # - removed session.begin due to deadlocks
-    # - fix off-by-one error and overflow
-    @synchronized(named("select_subnet"))
     def select_subnet(self, context, net_id, ip_address, segment_id,
                       subnet_ids=None, **filters):
         LOG.info("Selecting subnet(s) - (Step 2 of 3) [{0}]".format(