INFRA-124 - civibuild - Generate/save SITE_TOKEN

This will be useful for validating the Webtests' DSN cookie
INFRA-124 - civibuild - Allow injecting options into civicrm.settings.php for CiviTest
INFRA-124 - civibuild - Allow injecting pre or post settings (via civicrm.settings.d, drupal.settings.d, etc)
INFRA-124 - civibuild - Add clone-create, clone-show, clone-destroy (skeletal code)
INFRA-124 - civibuild - Extract function _amp_snapshot_restore()
INFRA-124 - civibuild - Implement civibuild_clone_create, civibuild_clone_show, civibuild_clone_destroy
INFRA-124 - civibuild - When destroying a build, also destroy any cloned DBs
_amp_install_* - Fix concurrency bug
INFRA-124 - When using paratest, automatically setup multiple DBs using "civibuild clone-create"
INFRA-124 - Generate and accept cookie "civiConsts"

This allows DB configuration options to propagate from the test-tier to the web-tier.
INFRA-124 - 100-paratest-dsn.php - Allow CLI option to forcibly reset DB
composer.json, composer.lock - Add phpunit, paratest
INFRA-124 - clone-create - Don't recreate DB unless the snapshots have changed (or unless --force is specified)
Merge pull request #81 from totten/master-civitest

INFRA-124 - Support for paratest