dev-manual: Added -ptest to list of complementarty packages

dev-manual: Added -ptest to list of complementarty packages

Added the '-ptest' complementary package to the list of packages,
which included '-dev' and '-dbg' when using inherit packagegroup.
Robert P. J. Day pointed out the code in the OE packagegroup.bbclass
class that showed these three packages all together.

Reported-by: Robert P. J. Day <rpjday@crashcourse.ca>
(From yocto-docs rev: 823555ac44958995426cc631d992b9d276c42ca4)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>