sysroot: add BUILD_SYSROOT envrionment value for sysroot
sysroot: add BUILD_SYSROOT envrionment value for sysroot

this patch adds environment value for sysroot
if BUILD_SYSROOT is set to 'true', add package list for development
when generating sysroot

Change-Id: Ie07b354cb76808e45608ac95772d2ed43b3ec541
Signed-off-by: Jae-young Hwang <5e42eac44e565adc88c63aa294a919bca487d0f7@samsung>

SamsungARTIK/build-artik