Adding Keystone to MDG Dockerfiles

Included environment files.
Admin password selection and storage needs to be discussed.

Change-Id: Ibcaa818bcc3ae6fd013507b0b114b15b70e60150
Signed-off-by: Eduardo Sousa <esousa@whitestack.com>
diff --git a/installers/docker/__keystone-db__.env b/installers/docker/__keystone-db__.env
new file mode 100644
index 0000000..ac2a8d8
--- /dev/null
+++ b/installers/docker/__keystone-db__.env
@@ -0,0 +1 @@
+MYSQL_ROOT_PASSWORD=__MYSQL_ROOT_PASSWORD__