Check if flavor id is an empty string

Now once a flavor is created with empty string id, its id and
name cannot be specified when we use or delete the flavor.

This checks if flavorid is empty when creating a new flavor.
And if so, assigns auto-generated flavorid.

Fixes bug: 1148563

Change-Id: Ib48c4cc4ebd993d1f3f3d60a7bb856eff3c279d5
Merge "Check if flavor id is an empty string"
Merge remote-tracking branch 'm_src_repo/master' into build-temp