Low: ocf_shellfuncs: set OCF_RESOURCE_INSTANCE to "RESOURCE_ID" for meta-data

Resource agents often have parameters whose default values include the
resource instance. Current approaches to representing that have various
deficiencies. Defaulting OCF_RESOURCE_INSTANCE to "RESOURCE_ID" for meta-data
actions allows agents to use ${OCF_RESOURCE_INSTANCE} in meta-data defaults
and get something useful (UIs that know the instance name can pass it,
and those that don't will get a fairly understandable string).