Increase default swift storage

Swift storage is used as glance image back-end. Tempest have cinder to
uploads 1 GiB image from cinder in twice.

In parallel execution in cause an issue, bacuse the current default size is
1_000_000 KiB.

Increasing the default swit storage size from 1_000_000 KiB 4_000_000
KiB when tempest is enabled.

Fixing bug 1225664

Change-Id: Iccd6368e4df71abb5ccfe7d361c64d86e1071d35

lib/swift

@@ -55,7 +55,13 @@ fi
 # swift data. Set ``SWIFT_LOOPBACK_DISK_SIZE`` to the disk size in
 # kilobytes.
 # Default is 1 gigabyte.
-SWIFT_LOOPBACK_DISK_SIZE=${SWIFT_LOOPBACK_DISK_SIZE:-1000000}
+SWIFT_LOOPBACK_DISK_SIZE_DEFAULT=1048576
+# if tempest enabled the default size is 4 Gigabyte.
+if is_service_enabled tempest; then
+    SWIFT_LOOPBACK_DISK_SIZE_DEFAULT=${SWIFT_LOOPBACK_DISK_SIZE:-4194304}
+fi
+
+SWIFT_LOOPBACK_DISK_SIZE=${SWIFT_LOOPBACK_DISK_SIZE:-$SWIFT_LOOPBACK_DISK_SIZE_DEFAULT}
 
 # Set ``SWIFT_EXTRAS_MIDDLEWARE`` to extras middlewares.
 # Default is ``staticweb, tempurl, formpost``