Run setup commands in a single process #378

Many scenarios create their fixtures with a series of When I run steps before the actual test starts: posts, terms, users, comments, menu items, widgets, transients, cron events or attachments. Each of these steps starts a new PHP process and loads WordPress, which costs about 0.3 seconds.

Across the bundled commands, about 550 of these setup commands per suite run could share a process with the one before them.

A step that runs a list of setup commands in a single process, while still allowing their output to be saved into variables, would reduce each setup block to one WordPress bootstrap.