wp-now detects wp-content mode if there is a mu-plugins subdir inside the dir where it is executed.

[MocioF]

In wp-now docs it is written:
### Automatic Modes
wp-now automatically operates in a few different modes for both the start and the php commands. The selected mode depends on the directory in which it is executed:
[...]
- plugin, theme, or wp-content
[...]
-- wp-content mode: Presence of plugins and themes subdirectories.
[...]
However, it detects wp-content mode even if it is run in a directory without plugins or themes subdirectories but with a mu-plugins subdiderctory.

[adamziel]

cc @sejas @wojtekn