oeqa/target/ssh: Ensure EAGAIN doesn't truncate output

We have a suspicion that the read() call may return EAGAIN on the non-blocking
fd and this may truncate test output leading to some of our intermittent failures.
Tweak the code to avoid this potential issue.

(From OE-Core rev: 605d832e86f249100adaf3761b4e1701401d0b76)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit a8920c105725431e989cceb616bd04eaa52127ec)
Signed-off-by: Steve Sakoman <steve@sakoman.com>

meta/lib/oeqa/core/target/ssh.py

@@ -226,6 +226,9 @@ def SSHCall(command, logger, timeout=None, **opts):
                             endtime = time.time() + timeout
                 except InterruptedError:
                     continue
+                except BlockingIOError:
+                    logger.debug('BlockingIOError')
+                    continue
 
             # process hasn't returned yet
             if not eof: