HBASE-19771 restore_snapshot shell command gives wrong namespace if the namespace doesn't exist

Signed-off-by: tedyu <yuzhihong@gmail.com>

hbase-shell/src/main/ruby/shell/commands.rb

@@ -117,7 +117,8 @@ module Shell
           raise "Unknown region #{args.first}!"
         end
         if cause.is_a?(org.apache.hadoop.hbase.NamespaceNotFoundException)
-          raise "Unknown namespace #{args.first.split(':')[0]}!"
+          s = /.*NamespaceNotFoundException: (?<namespace>[^\n]+).*/.match(cause.message)
+          raise "Unknown namespace #{s['namespace']}!"
         end
         if cause.is_a?(org.apache.hadoop.hbase.snapshot.SnapshotDoesNotExistException)
           raise "Unknown snapshot #{args.first}!"