reduce the height of the textarea to 4

Textarea of height 10 lines seems large considering the usecases
in Horizon for forms containing multiple fields. Reducing it to a
lesser value for subnet workflows in networks and images forms.

Change-Id: I99dc6f735ed446ff4005aac7a981461c236f65b9
Closes-Bug: 1358856
Merge "reduce the height of the textarea to 4"