[PATCH for-4.15] automation: Fix containerize to understand the Alpine container

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

This was missing from the work to add the alpine container.

Fixes: a9afe7768bd ("automation: add alpine linux 3.12 x86 build container")
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Wei Liu <wl@xxxxxxx>
CC: Doug Goldstein <cardoe@xxxxxxxxxx>
CC: Ian Jackson <iwj@xxxxxxxxxxxxxx>

For 4.15.  This is only developer tooling, with no impact on the build.
---
 automation/scripts/containerize | 1 +
 1 file changed, 1 insertion(+)

diff --git a/automation/scripts/containerize b/automation/scripts/containerize
index da45baed4e..b7c81559fb 100755
--- a/automation/scripts/containerize
+++ b/automation/scripts/containerize
@@ -24,6 +24,7 @@ die() {
 #
 BASE="registry.gitlab.com/xen-project/xen"
 case "_${CONTAINER}" in
+    _alpine) CONTAINER="${BASE}/alpine:3.12" ;;
     _archlinux|_arch) CONTAINER="${BASE}/archlinux:current" ;;
     _centos7) CONTAINER="${BASE}/centos:7" ;;
     _centos72) CONTAINER="${BASE}/centos:7.2" ;;
-- 
2.11.0