Rename Extra Specs with Metadata in Flavors table

The 'Extra Specs' column heading in the Flavors table has been renamed
to 'Metadata' for consistency (for example, 'Update Metadata' form)

Closes-Bug: #1371251

Change-Id: Ibeb81167553b42f299613359dad49a9bff05fc48
Merge "Rename Extra Specs with Metadata in Flavors table"