Update README for v1.4.0 release

Update README for v1.4.0 release

Update README for v1.4.0 release

Bump kernel to 4.15.9

Reduce the memory consumption at startup (rancher#2247)

Offline image is automatically loaded when the system boots.
When the system memory is not large enough (such as 1G), will lead to
kernel panic.

Reduce the memory consumption at startup (rancher#2247)

Offline image is automatically loaded when the system boots.
When the system memory is not large enough (such as 1G), will lead to
kernel panic.

Bump to kernel 4.9.78-rancher2

Fix verbose output for ramdisk info

Fix a typo path for rpi kernel url

Make sure we can control whether INTEGRATION-TEST is executed

Make sure we can control whether INTEGRATION-TEST is executed