fix: Handle stderr properly in SSH transport

[kadler]

Instead of reading a small amount of data in a blocking way from the
stdout and stderr streams, enable non-blocking I/O and attempt to read
as much data as possible. In addition, make a convenience function to
handle the stream being closed and timeouts so that we don't need to
store a temp variable in the loop. This prevents the situation that lead
to issue #74 where the stderr data is written to the output XML if
stdout is already closed.

Fixes #74

[NattyNarwhal]

this looks right? before

***********************
control Fri Feb  3 15:56:19 2023
 ipc(*na) ctl(*here *cdata)
input Fri Feb  3 15:56:19 2023
<?xml version='1.0'?>
<xmlservice><sh error="fast" var="wrkactjob"><![CDATA[/QOpenSys/usr/bin/system WRKACTJOB]]></sh></xmlservice>

output Fri Feb  3 15:56:20 2023
b' directory\n'
parse (fail) Fri Feb  3 15:56:20 2023
parse step: 3 (1-ok, 2-*BADPARSE, 3-*NOPARSE)
{'error': {'error': '*NOPARSE', 'wrkactjob': {...}}}

after

***********************
control Fri Feb  3 15:59:39 2023
 ipc(*na) ctl(*here *cdata)
input Fri Feb  3 15:59:39 2023
<?xml version="1.0" ?><xmlservice><sh var="wrkactjob" error="fast"><![CDATA[/QOpenSys/usr/bin/system WRKACTJOB]]></sh></xmlservice>
output Fri Feb  3 15:59:40 2023
<?xml version='1.0'?>
<xmlservice>
<error>*NODATA</error>
</xmlservice>
parse step: 1 (1-ok, 2-*BADPARSE, 3-*NOPARSE)

[kadler]

Merged in e16b965