[DSH] Delete hardcoded image name

We have a debian 8 image for a long time, which
can be successfully used by docker standalone host
to run dockerized apps, but we still don't use it.
This commit deletes hardcode and adds image field to
ui with filter by type `linux.docker`.

Change-Id: Ie3d9d454cd98f651833b28690d33d55b404dc13d

DockerStandaloneHost/elements/readme.rst

@@ -33,6 +33,16 @@ On Centos, Fedora:
 Image building
 --------------
 
+To build Debian-based image
+
+.. sourcecode:: bash
+
+   sudo ELEMENTS_PATH=${murano_agent_root}/contrib/elements:${murano_apps_root}/Docker/DockerStandaloneHost/elements \
+       DIB_RELEASE=jessie DIB_CLOUD_INIT_DATASOURCES="Ec2, ConfigDrive, OpenStack" disk-image-create vm debian murano-agent-debian \
+       docker -o debian8-x64-docker
+
+To build Ubuntu-based image
+
 .. sourcecode:: bash
 
     sudo ELEMENTS_PATH=${murano_agent_root}/contrib/elements:${murano_apps_root}/Docker/DockerStandaloneHost/elements disk-image-create \

DockerStandaloneHost/package/UI/ui.yaml

@@ -24,7 +24,7 @@ Application:
       type: io.murano.resources.LinuxMuranoInstance
     name: generateHostname($.instanceConfiguration.unitNamingPattern, 1)
     flavor: $.instanceConfiguration.flavor
-    image: 'ubuntu14.04-x64-docker'
+    image: $.instanceConfiguration.image
     keyname: $.instanceConfiguration.keyPair
     assignFloatingIp: $.appConfiguration.assignFloatingIP
     availabilityZone: $.instanceConfiguration.availabilityZone
@@ -80,6 +80,13 @@ Forms:
           required: false
           hidden: true
           description: Specify some instance parameters on which the application would be created
+        - name: image
+          type: image
+          imageType: linux.docker
+          label: Instance image
+          description: >-
+            Select valid image for the application. Image should already be prepared and
+            registered in glance.
         - name: flavor
           type: flavor
           label: Instance flavor