Meta Environment: bin/import-plugin.php should be able to create Plugin Posts

[dd32]

It's been pointed out that bin/import-plugin.php in the Meta Environment can only import plugins which already exist in it's Database, this isn't terribly useful for testing development environments.

The attached patch adds a --create flag which allows the script to create a post in the event it doesn't already exist.
This flag should never be set/used in production, as the posts should already exist there (from the upload process).

[dd32]

In 8728:

Plugin Directory: Bin: Add an optional --create argument to the import script to aid debugging in the Meta Environment.

In production, the posts are created automatically upon upload, and this argument should never be needed (Unless someone manually creates the SVNs and then needs to import it to the directory).

Fixes #4377.