[TEST] Delete registered queries to prevent <PercolatorIntegrationTest> failures

Potentially, prepare deleting the whole `_percolator` index on Travis-CI

Verified with:

Download or clone this [gist](https://gist.github.com/4239703):

    git clone git://gist.github.com/4239703.git elasticsearch_vagrant && cd elasticsearch_vagrant

Run bundle install, etc. Then, configure ES:

    echo '
    {
      "elasticsearch" : {
        "cluster_name" : "elasticsearch_test_in_vagrant",
        "index_shards" : 1,
        "index_replicas" : 0
      }
    }' > node.json

Install Ruby 1.9.3, _Tire_, etc:

    echo '
    # Install the Tire Rubygem
    apt-get install make git libcurl3 libcurl3-gnutls libcurl4-openssl-dev libsqlite3-dev -y
    apt-get install redis-server  -y
    apt-get install ruby1.9.3 -y
    update-alternatives --set ruby /usr/bin/ruby1.9.1
    gem install bundler --no-rdoc --no-ri
    test -d "tire" || git clone git://github.com/karmi/tire.git
    chown -R vagrant:staff tire
    cd tire
    bundle install
    ' > install.sh

Build and provision the machine:

    NODE_CONFIG=node.json INSTALL=install.sh time bundle exec vagrant up

Run the Tire tests:

    echo '
    cd tire

    echo "Running Tire tests in '`pwd`'"
    echo "Ruby: `ruby -v`"
    echo "Java: `java -version 2>&1 | head -1`"

    for i in {1..5}
      do
        echo "-------------------------------------------------------------------------------"
        echo "TEST $i"
        echo "-------------------------------------------------------------------------------"
        time bundle exec rake test
      if [ $? == 0 ]; then echo "$i: OK" >> results.txt; else echo "$i: FAIL">> results.txt; fi
    done

    echo; echo; echo "==============================================================================="
    cat results.txt
    ' > run_tire_tests.sh

    cat run_tire_tests.sh | xargs -0 bundle exec vagrant ssh -c

Related: #537

Closes #541