Enforce FlavorExtraSpecs Key format.

When creating a key name with characters like '/' that are not
being encoded or cannot be handled as expected by routes when
matching the url, then it's not possible to remove them anymore.
The new format apply the restriction: "[\w\.\- :]+$"

This change will fix the bug without API change.

Change-Id: I64bc098c4bde33c40fa149191a751ea3eb19f932
Closes-Bug: #1256119
Merge "Enforce FlavorExtraSpecs Key format."