bridge: expand ${libexecdir} in package manifests
bridge: expand ${libexecdir} in package manifests

Perform expansion of static variables when reading package files.  So
far we support exactly one variable: ${libexecdir}.

cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,mvollmer/cockpit,garrett/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,garrett/cockpit,garrett/cockpit,garrett/cockpit,garrett/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit