The`kick_off` method is broken for AndroidTarget

[marcbonnici]

The kick_off method with Android Target is currently broken, it either exhibits blocking behaviour on the command to be ran or fails to run the command correctly.

Example blocking behaviour reproducer:

from devlib import AndroidTarget
target = AndroidTarget()
target.kick_off('sleep 10; echo "Completed" > /sdcard/sleep.log')   # This command blocks until the command completes.

Example failure to execute reproducers:

target.kick_off('echo "Testing" > /sdcard/testing')
target.execute('cat /sdcard/testing')
"nohup: can't execute 'echo': No such file or directory\n"

target.kick_off('ls')
TargetTransientError: adb has returned early; did not get an exit code. Was kill-server invoked?
OUTPUT:
-----

0
nohup: appending output to nohup.out

-----
STDERR:
-----

-----

[douglas-raillard-arm]

So I had a go at it, here are my observations:

• SSH and Android have different kick_off() implementation

• The SSH version properly does not block in the first case

• The android version does block, because we lack a level of sh -c:

  (export PATH=/root/devlib-target/bin:$PATH && export LC_ALL=C && cd /root/devlib-target && /root/devlib-target/bin/busybox nohup sleep 10; echo "Completed" &) 2>&1

  and it should be:

  (export PATH=/root/devlib-target/bin:$PATH && export LC_ALL=C && cd /root/devlib-target && /root/devlib-target/bin/busybox nohup sh -c 'sleep 10; echo "Completed"' &) 2>&1

• This error is not so surprising as echo is a shell builtin. Often there is also a binary but I guess not always on android.

  "nohup: can't execute 'echo': No such file or directory\n"

• I could not reproduce this one but it's easily explained:

  target.kick_off('ls')
  TargetTransientError: adb has returned early; did not get an exit code. Was kill-server invoked?

  nohup wrote this line to stdout:

  nohup: appending output to nohup.out

  after the exit code. Unfortunately, adb_shell() parses the last line as the exit code :boom: . Should be easily fixable by redirecting nohup output to /dev/null

So overall I'd suggest:

• Getting rid of the per-target implementation. That is a generic feature that can be implemented on top of other generic features.
• The generic implementation should use nohup, but 1) redirect all output to /dev/null and 2) use quote(command) and interpolate that in sh -c {}.

2) will fix both the blocking issue and the shell builtin issue.