The goal of this refactoring is to have a single place where a ref
pattern is validated as regular expression. So far this was done in 2
places (in RefControl and in ProjectConfig). For validating a ref
pattern as regular expression we must remove placeholder variables
such as '${username}' because it would be an invalid regular
expression otherwise. We don't want to do this in several places
especially because we want to support further placeholder variables in
future.
Change-Id: I11c76e37f22233d89b631375ac6f2ef60f97801f
Signed-off-by: Edwin Kempin <ekempin@google.com>