add checks for timeouts attributes and blocks
add checks for timeouts attributes and blocks

Don't overwrite anything the provider defined, in order to maintain
existing behavior.

Change strings to pre-defined constants

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