ls: move builder/node status error msg below table

[crazy-max]

follow-up #830

as suggested in #764, display builder/node status error msg below table to avoid a messy output:

$ docker buildx ls
NAME/NODE       DRIVER/ENDPOINT                 STATUS   BUILDKIT PLATFORMS
builder *       docker-container
  builder0      unix:///var/run/docker.sock     running  b6924b0  linux/amd64, linux/arm64, linux/riscv64
  mac-mini-m1   tcp://mac-mini-m1.home.com:2376 running  b6924b0  linux/arm64*, linux/amd64
  sifive        tcp://sifive.home.com:2375      running  b6924b0  linux/riscv64*
builder2        docker-container
  builder20     unix:///var/run/docker.sock     inactive
graviton2       docker-container
  node1         ssh://ubuntu@18.216.87.142      Get "http://docker.example.com/v1.24/info": context deadline exceeded
desktop-linux                                   protocol not available
desktop-windows                                 protocol not available
default         docker
  default       default                         running                20.10.14 linux/amd64, linux/arm64, linux/riscv64, linux/ppc64le, linux/s390x, linux/386, linux/arm/v7, linux/arm/v6

now:

$ docker buildx ls
NAME/NODE       DRIVER/ENDPOINT                 STATUS   BUILDKIT PLATFORMS
builder *       docker-container
  builder0      unix:///var/run/docker.sock     running  b6924b0  linux/amd64, linux/arm64, linux/riscv64
  mac-mini-m1   tcp://mac-mini-m1.home.com:2376 running  b6924b0  linux/arm64*, linux/amd64
  sifive        tcp://sifive.home.com:2375      running  b6924b0  linux/riscv64*
builder2        docker-container
  builder20     unix:///var/run/docker.sock     inactive
graviton2       docker-container
  node1         ssh://ubuntu@18.216.87.142      error
desktop-linux                                   error
desktop-windows                                 error
default         docker
  default       default                         running  20.10.14 linux/amd64, linux/arm64, linux/riscv64, linux/ppc64le, linux/s390x, linux/386, linux/arm/v7, linux/arm/v6

Failed to get status for graviton2 (node1): Get "http://docker.example.com/v1.24/info": context deadline exceeded
Cannot load builder desktop-linux: protocol not available
Cannot load builder desktop-windows: protocol not available

will take a look for a progress tabwriter in a follow-up

Signed-off-by: CrazyMax crazy-max@users.noreply.github.com