cros_vm_lib: Increase qemu memory to 8G

We set the vm memory to 4G from 2012. Increase the value of the memory
to 8G by default as 6 years has passed.

BUG=chromium:800554
TEST=./bin/cros_start_vm --board=betty --kvm_ram=16G --image_path=chromiumos_qemu_image.bin
TEST=./bin/cros_start_vm --board=betty --image_path=chromiumos_qemu_image.bin

Change-Id: I36f470c542bdf68b2a7beca861da17302b5b8a22
Reviewed-on: https://chromium-review.googlesource.com/872226
Reviewed-by: Ilja H. Friedel <ihf@chromium.org>
Tested-by: Ilja H. Friedel <ihf@chromium.org>
Commit-Queue: Po-Hsien Wang <pwang@chromium.org>
1 file changed