Change the number of workspaces use command line

To get the current values:

dconf read /org/compiz/profiles/unity/plugins/core/hsize
dconf read /org/compiz/profiles/unity/plugins/core/vsize

To set new values:

dconf write /org/compiz/profiles/unity/plugins/core/hsize 4

dconf write /org/compiz/profiles/unity/plugins/core/vsize 1