oeqa/core/target/ssh.py: increase maximum read bytes from 1024 to 4096

When running testimage task for core-image-sato-sdk, the following
error appeared.

  UnicodeDecodeError: 'utf-8' codec can't decode byte 0x82 at position 0: invalid start byte

Checking the codes, I found it's caused by setting a 1024 limit for the
read method of the StreamReader object.

Comments from the manual:
"""
The chars argument indicates the number of decoded code points or bytes to
return. The read() method will never return more data than requested, but
it might return less, if there is not enough available.
"""

When running `systemctl status --full' on target, this error occurs.

This patch increase the bytes limit to 4096 to fix the error.

(From OE-Core rev: f1fad60ae3be4450aca6058d5665fb10a9148b44)

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

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

@@ -208,7 +208,7 @@ def SSHCall(command, logger, timeout=None, **opts):
                 try:
                     if select.select([process.stdout], [], [], 5)[0] != []:
                         reader = codecs.getreader('utf-8')(process.stdout)
-                        data = reader.read(1024, 1024)
+                        data = reader.read(1024, 4096)
                         if not data:
                             process.stdout.close()
                             eof = True