Use $(shell pwd) rather than $(pwd)

Change-Id: I34b90ec8761d9368bad226810e75a42099ad4afb
Reviewed-on: http://review.couchbase.org/28202
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>