[fix] Workaround channel.recv_exit_status not accepting timeout param

[asmodehn]

Checklist

• I have read the OpenWISP Contributing Guidelines.
• I have manually tested the changes proposed in this pull request.
• I have written new test cases for new code and/or updated existing tests for changes to existing code.
• I have updated the documentation.

Reference to Existing Issue

Addresses openwisp/openwisp-firmware-upgrader#244 (comment)

Description of Changes

Paramiko recv_exit_status() doesnt accept timeout as parameter, and might wait until deconnection, even if that is not necessary.

This is a three line workaround that problem that only wait the SSH_COMMAND_TIMEOUT

[asmodehn]

I guess an improvement could be to wait only the time left in SSH_COMMAND_TIMEOUT after the command is run, but that might be add a bit of logic to exec_command...

[coveralls]

coverage: 98.744% (-0.02%) from 98.759%
when pulling 24ec502 on asmodehn:fix_ignored_command_timeout
into 3a45fd9 on openwisp:master.

[asmodehn]

FYI : It looks like, after this change, we could get rid of the subprocess there: https://github.com/openwisp/openwisp-firmware-upgrader/blob/master/openwisp_firmware_upgrader/upgraders/openwrt.py#L414
I understand it becomes redundant ?

[nemesifier]

FYI : It looks like, after this change, we could get rid of the subprocess there: https://github.com/openwisp/openwisp-firmware-upgrader/blob/master/openwisp_firmware_upgrader/upgraders/openwrt.py#L414 I understand it becomes redundant ?

I had to implement it using subprocess because in old openwrt versions sysupgrade just hanged, it was so annoying.

Maybe with this solution, we won't need to do that anymore, we'll have to test.