Support exec.d Paths
Support exec.d Paths

Shell free profile.d, otherwise known as exec.d will be added to the
specification.  This change updates the library to return the paths for files
that will be added to the specified directory.

[buildpacks/rfcs#104]

Signed-off-by: Ben Hale <cf6bfba6a9cc3ab14105263f6e4be417b99c9860@vmware.com>

buildpacks/libcnb