Docker: switch to alpinelinux and cpm

Change-Id: I78210b14a3620fcba36ee7a49f83cd5cd8acc1f3
diff --git a/.gitignore b/.gitignore
index 8107e76..1336b0e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -20,5 +20,4 @@
 **/LOG
 **/LOG.old.*
 example-models/wpd19_10000/wpd19_10000.rocksdb/LOG
-
-
+!.dockerignore