Create Perflab_Background_Process::run method

Create a new a Perflab_Background_Process class to handle the background process runs.

This class will contain other helper methods for running jobs the background process built out in other issues.

• Create Background Processing Infrastructure: Create Perflab_Background_Process::memory_exceeded method #493
• Create Background Processing Infrastructure: Create Perflab_Background_Process::time_exceeded method #494

Acceptance Criteria

• Create a new run( int $job_id ) method in the Perflab_Background_Process class.
• The method will run through the following steps sequentially.

1. Set the start time
   A $start_time variable is set using the current timestamp as the value.

2. Lock the process

• The job process is locked by setting a term meta against the job term. The meta key will be job_lock and the value the current timestamp.
• The job status is also updated by setting the job_status meta to running

3. Retrieve the job information
   Using the $job_id passed to the run method get the following information.

• $job - Create a new Job object using the Perflab_Background_Job class
• $job_name this is the the job terms slug
• $job_data this is from the job_data term meta

4. Call the job action
   Within a do/while loop call do_action( 'perflab_job_' . $job_name, $job_id, $job_data );

The while loop conditions will call the following like so:
while( ! $this->memory_exceeded() && ! $this->time_exceeded() && ! $job->is_completed( $job_id ) )

5. Unlock process
   Outside of the while loop, to end the process, unlock the job by removing the job_lock term meta.

6. Start the next batch process
   Start the next batch process by calling the function perflab_background_process_next_batch() passing the $job_id as the only parameter.