fleetctl: destroy using wildcards can search in the repository

Curerntly, fleetctl destroy *.service, it will search the units
in the local directory. The args with wildcards have already parsed
by golang package before be passed into runDestroyUnits. So
runDestroyUnits cannot do anything.

This patch support wildcards just search in the repository,
not from local directory. But need support a new interface. The new
interface is:
    fleetctl destroy "xx*.service".
We found that if bracket the service name, the arg will not be
parsed by golang package to local directory. Then we can do match it
with the service name in the repository.

Fixes coreos#710

fleetctl/destroy.go

@@ -14,6 +14,10 @@
 
 package main
 
+import (
+	"path"
+)
+
 var cmdDestroyUnit = &Command{
 	Name:    "destroy",
 	Summary: "Destroy one or more units in the cluster",
@@ -29,14 +33,27 @@ Destroyed units are impossible to start unless re-submitted.`,
 }
 
 func runDestroyUnits(args []string) (exit int) {
+	states, err := cAPI.UnitStates()
+	if err != nil {
+		stderr("Error retrieving list of units from repository: %v", err)
+		return 1
+	}
+
 	for _, v := range args {
 		name := unitNameMangle(v)
-		err := cAPI.DestroyUnit(name)
-		if err != nil {
-			continue
-		}
+		for _, us := range states {
+			if match, _ := path.Match(name, us.Name); match == false {
+				continue
+			}
+
+			err = cAPI.DestroyUnit(us.Name)
+			if err != nil {
+				stderr("Error destroying unit %s: %v", us.Name, err)
+				continue
+			}
 
-		stdout("Destroyed %s", name)
+			stdout("Destroyed %s", us.Name)
+		}
 	}
 	return
 }