With latest terraform getting deprecated warnings for interpolation syntax

[yussufsh]

With TF v0.13.4 started getting the interpolation syntax warnings. This will show up during apply and validate commands.

# ./terraform version
Terraform v0.13.4

# terraform validate

Warning: Interpolation-only expressions are deprecated

  on variables.tf line 177, in locals:
 177:     private_key_file    = var.private_key_file == "" ? "${path.cwd}/data/id_rsa" : "${var.private_key_file}"

Terraform 0.11 and earlier required all non-constant expressions to be
provided via interpolation syntax, but this pattern is now deprecated. To
silence this warning, remove the "${ sequence from the start and the }"
sequence from the end of this expression, leaving just the inner expression.

Template interpolation syntax is still used to construct strings from
expressions when the template includes multiple interpolation sequences or a
mixture of literal strings and interpolations. This deprecation applies only
to templates that consist entirely of a single interpolation sequence.

(and 3 more similar warnings elsewhere)

Success! The configuration is valid, but there were some validation warnings as shown above.