core: include "root" element when constructing legacy ModuleState path
core: include "root" element when constructing legacy ModuleState path

We've not yet adjusted any of the state structs to reflect our new address
types because they are used with encoding/json to produce our state file
format, but the shimming here previously was incorrect because it failed
to include the special "root" string that's always required at element
zero of a module path in the state.

mattray/terraform,drebes/terraform,brandontosch/terraform,VladRassokhin/terraform,youhong316/terraform,brandontosch/terraform,iljaskevic/terraform,brandontosch/terraform,mattray/terraform,tpounds/terraform,heimweh/terraform,drebes/terraform,iljaskevic/terraform,rnaveiras/terraform,tpounds/terraform,tommynsong/terraform,gechr/terraform,mattray/terraform,heimweh/terraform,hashicorp/terraform,tommynsong/terraform,pryorda/terraform,brandontosch/terraform,pryorda/terraform,ewbankkit/terraform,pryorda/terraform,pdecat/terraform,ewbankkit/terraform,youhong316/terraform,heimweh/terraform,VladRassokhin/terraform,gechr/terraform,VladRassokhin/terraform,drebes/terraform,iljaskevic/terraform,nlamirault/terraform,heimweh/terraform,luis-silva/terraform,rnaveiras/terraform,luis-silva/terraform,nlamirault/terraform,tommynsong/terraform,pdecat/terraform,youhong316/terraform,hashicorp/terraform,youhong316/terraform,hashicorp/terraform,apparentlymart/terraform,iljaskevic/terraform,pradeepbhadani/terraform,apparentlymart/terraform,apparentlymart/terraform,pradeepbhadani/terraform,ewbankkit/terraform,tpounds/terraform,heimweh/terraform,luis-silva/terraform,gechr/terraform,pdecat/terraform,drebes/terraform,apparentlymart/terraform,VladRassokhin/terraform,tpounds/terraform,nlamirault/terraform,brandontosch/terraform,pradeepbhadani/terraform,ewbankkit/terraform,rnaveiras/terraform,pdecat/terraform,apparentlymart/terraform,mattray/terraform,luis-silva/terraform