buildroot

lighttpd: carry common keywords out to variables

S50lighttpd contains repeating keywords that are worth carrying out as
variables: pid file name, daemon name, config file name.

Signed-off-by: Philipp Skadorov <philipp.skadorov@savoirfairelinux.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>