Restore human-friendly plan output.

When an unexpected diff occurs, return the human-readable plan output,
instead of JSON.

A previous version of terraform-plugin-test/terraform-exec didn't
support reading the non-JSON plan file. Update to latest to have the
function do what it was meant to.

go.mod

@@ -26,9 +26,9 @@ require (
 	github.com/hashicorp/go-version v1.2.1
 	github.com/hashicorp/hcl/v2 v2.3.0
 	github.com/hashicorp/logutils v1.0.0
-	github.com/hashicorp/terraform-exec v0.9.0
+	github.com/hashicorp/terraform-exec v0.10.0
 	github.com/hashicorp/terraform-json v0.5.0
-	github.com/hashicorp/terraform-plugin-test/v2 v2.1.1
+	github.com/hashicorp/terraform-plugin-test/v2 v2.1.2
 	github.com/hashicorp/yamux v0.0.0-20181012175058-2f1d1f20f75d // indirect
 	github.com/keybase/go-crypto v0.0.0-20161004153544-93f5b35093ba
 	github.com/kylelemons/godebug v1.1.0 // indirect

go.sum

@@ -191,12 +191,12 @@ github.com/hashicorp/hcl/v2 v2.3.0 h1:iRly8YaMwTBAKhn1Ybk7VSdzbnopghktCD031P8ggU
 github.com/hashicorp/hcl/v2 v2.3.0/go.mod h1:d+FwDBbOLvpAM3Z6J7gPj/VoAGkNe/gm352ZhjJ/Zv8=
 github.com/hashicorp/logutils v1.0.0 h1:dLEQVugN8vlakKOUE3ihGLTZJRB4j+M2cdTm/ORI65Y=
 github.com/hashicorp/logutils v1.0.0/go.mod h1:QIAnNjmIWmVIIkWDTG1z5v++HQmx9WQRO+LraFDTW64=
-github.com/hashicorp/terraform-exec v0.9.0 h1:NmCtcsnmPBU6P3cDeKD26bD72evsMhmuDLvuNRgrTHc=
-github.com/hashicorp/terraform-exec v0.9.0/go.mod h1:tOT8j1J8rP05bZBGWXfMyU3HkLi1LWyqL3Bzsc3CJjo=
+github.com/hashicorp/terraform-exec v0.10.0 h1:3nh/1e3u9gYRUQGOKWp/8wPR7ABlL2F14sZMZBrp+dM=
+github.com/hashicorp/terraform-exec v0.10.0/go.mod h1:tOT8j1J8rP05bZBGWXfMyU3HkLi1LWyqL3Bzsc3CJjo=
 github.com/hashicorp/terraform-json v0.5.0 h1:7TV3/F3y7QVSuN4r9BEXqnWqrAyeOtON8f0wvREtyzs=
 github.com/hashicorp/terraform-json v0.5.0/go.mod h1:eAbqb4w0pSlRmdvl8fOyHAi/+8jnkVYN28gJkSJrLhU=
-github.com/hashicorp/terraform-plugin-test/v2 v2.1.1 h1:aATRyyPlEKkFYUweD2Hld9eep77qzJVu8wg0mgyUE50=
-github.com/hashicorp/terraform-plugin-test/v2 v2.1.1/go.mod h1:HaW2G5cDTVyiEKt7PHC85YSM5BwvYl/rIko1g8Lg7qE=
+github.com/hashicorp/terraform-plugin-test/v2 v2.1.2 h1:p96IIn+XpvVjw7AtN8y9MKxn0x69S7wtbGf7JgDJoIk=
+github.com/hashicorp/terraform-plugin-test/v2 v2.1.2/go.mod h1:jerO5mrd+jVNALy8aiq+VZOg/CR8T2T1QR3jd6JKGOI=
 github.com/hashicorp/yamux v0.0.0-20180604194846-3520598351bb/go.mod h1:+NfK9FKeTrX5uv1uIXGdwYDTeHna2qgaIlx54MXqjAM=
 github.com/hashicorp/yamux v0.0.0-20181012175058-2f1d1f20f75d h1:kJCB4vdITiW1eC1vq2e6IsrXKrZit1bv/TDYFGMp4BQ=
 github.com/hashicorp/yamux v0.0.0-20181012175058-2f1d1f20f75d/go.mod h1:+NfK9FKeTrX5uv1uIXGdwYDTeHna2qgaIlx54MXqjAM=