Ignore key/value pairs with empty keys in workflow generation

Savanna should ignore key/value pairs with empty keys when
generating <property> tags or equal-separated dictionary
entries in workflow.xml.

Partial-bug: #1269972
Change-Id: I327d1f4ac2f5db3a2778678567b63148f41c7932
Merge "Ignore key/value pairs with empty keys in workflow generation"