Issue #37: PID file directory is now a module param

[tux-o-matic]

Fixes #37. Users of this module now have the option to set a different directory for the PID file of the various Dynatrace services. The default is still '/tmp' but is recommended to be overwritten to something like:

dynatrace::pid_file_directory: '/var/run/dynatrace'

With this PR, if the value is overwritten to be something else than '/tmp', the Puppet module will ensure that the directory exists via a File resource. To ensure that the service status is still working during the migration, the services should be stopped or the pid files copied from /tmp to the new directory before running Puppet with a different value than '/tmp'.