ffdc: Trigger paramiko exec_command() timeout mechanism

Add data read/write operation to trigger paramiko exec_command() timeout mechanism.
Reading channel status does not activate the timeout mechanism.

Test:
- Regression test to openbmc, ubuntu, rhel with standard config and plugins

Change-Id: Ib65304dbbfc1f2df592296e5b5025c928cef86d4
Signed-off-by: Peter D  Phan <peterp@us.ibm.com>
diff --git a/ffdc/lib/ssh_utility.py b/ffdc/lib/ssh_utility.py
index 137fd79..ea5cf4f 100644
--- a/ffdc/lib/ssh_utility.py
+++ b/ffdc/lib/ssh_utility.py
@@ -90,6 +90,10 @@
                 self.sshclient.exec_command(command, timeout=default_timeout)
             start = time.time()
             while time.time() < start + default_timeout:
+                # Need to do read/write operation to trigger
+                # paramiko exec_command timeout mechanism.
+                xresults = stdout.readlines()
+                results = ''.join(xresults)
                 if stdout.channel.exit_status_ready():
                     break
                 time.sleep(1)
@@ -100,7 +104,7 @@
             out = ''
             for item in stderr.readlines():
                 err += item
-            for item in stdout.readlines():
+            for item in results:
                 out += item
 
             return cmd_exit_code, err, out