baseqtversion: use environment in ensureMkSpecParsed

Task-number: QTCREATORBUG-10695
Change-Id: I4a61cc03f0aa978d07d48e8f56f032a7a666879b
Reviewed-by: David Kaspar <dkaspar@blackberry.com>
Reviewed-by: Daniel Teske <daniel.teske@digia.com>