修改croot实现cout可以快速进入输出目录

在build/envsetup.sh中，参照croot()的实现，实现了新的cout功能，可以快速切换到产品输出目录。

function cout()

{

T=$(gettop)

if [ "$T" ]; then

if [ "$ANDROID_PRODUCT_OUT" ]; then

cd $ANDROID_PRODUCT_OUT

else

echo "Couldn't locate the out directory. Try use lunch first "

fi

else

echo "Couldn't locate the top of the tree. Try setting TOP."

fi

}