devtool: modify: Handle recipes with a menuconfig task correctly

This avoids the following error when running `devtool modify` on a
recipe that has a menuconfig task, but does not have
KCONFIG_CONFIG_ENABLE_MENUCONFIG set.

  .../temp/run.do_configure.4163366: line 152:
  ${@ oe.types.boolean('${KCONFIG_CONFIG_ENABLE_MENUCONFIG}') }: bad substitution
  WARNING: .../temp/run.do_configure.4163366:152 exit 1 from
  '[ ${@ oe.types.boolean('${KCONFIG_CONFIG_ENABLE_MENUCONFIG}') } = True ]'

Signed-off-by: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit e87e6fa8)
Signed-off-by: Steve Sakoman <steve@sakoman.com>