Refer to,I had run a test case in real board successfully
The nfsrootfs image is too big ,it took too many download time in every test. So I put kernel  nfs and dtb image files on  tftp server,  then delete deploy action and add a few boot action commands to specify tftp addr...   The parameters(login_prompt&usrname&prompts) of the boot action are same with success version(has deploy action):
- boot:
    connection: telnet localhost 7000
    method: u-boot
    ##note the fellow commands lines is new added,the success version(has deploy action)that commands line is only "commands:nfs"
    - setenv serverip
    - tftp 0x8...0000 zImage_arm_1
    - tftp 0x4...0000 dtb_arm_1 
    - setenv nfsroot  rootfs_1
    - boot
      login_prompt: "arm login:"
      username: root
    - root@arm:~#
      minutes: 3
After job submited,the log display that kernel startup and rootfs  mount ok,  but  it always failed at login error.
error log lines:
err info:lava-test-shell: Wait for prompt ['root@arm:~#', 'Login incorrect', 'Login timed out', 'lava-test: # '] (timeout 00:05:00)
Nothing to run. Maybe the 'deploy' stage is missing, otherwise this is a bug which should be reported.

In addition£¬ does the uboot prompts(u-boot=>) no need to describe in boot action section? In other words the prompts auto_login is only described for kernel?