atc: update exec's check w/ err wraping
atc: update exec's check w/ err wraping

by wrapping the errors we can get abetter sense (from a higher level) of
the chain of errors that lead to it - this is a pattern that we've been
using as of go 1.13 coming out with updates to the `errors` and `fmt`
package that allows us to do so.

ref: https://blog.golang.org/go1.13-errors

Signed-off-by: Ciro S. Costa <4f5054ab2db051d03adf9068233a850c82b24437@pivotal.io>

concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse