Validate asec names.

Make sure asec names only contain alphanumeric, underscores,
dots, or dashes. Don't allow double dots.

Bug: 12504045

(cherry picked from commit 669626096513cf741646cf18a9e8ba246d359596)

Change-Id: Ia9d04f373aa95878b2e81584c4167dc2d4aa0c78