Fix mysql::sql task error message

Because of misplaced `"` no interpolation of the error message was
actually taking place.  After fixing this, the `Lint/UselessAssignment`
rubocop violation that had been disabled goes away too.

Author: alexjfisher

tasks/sql.rb

@@ -8,8 +8,8 @@ def get(sql, database, user, password)
   cmd << "--database=#{database}" unless database.nil?
   cmd << "--user=#{user}" unless user.nil?
   cmd << "--password=#{password}" unless password.nil?
-  stdout, stderr, status = Open3.capture3(*cmd) # rubocop:disable Lint/UselessAssignment
-  raise Puppet::Error, _("stderr: ' %{stderr}') % { stderr: stderr }") if status != 0
+  stdout, stderr, status = Open3.capture3(*cmd)
+  raise Puppet::Error, _("stderr: '%{stderr}'" % { stderr: stderr }) if status != 0
   { status: stdout.strip }
 end