qemurunner: print tail qemu log in case bootlog is empty

There are cases where the 'while loop' waiting for login prompt fails
and the bootlog variable does not get populated, thus use the the new
qemurunner member (self.msg) which stores all output coming from the qemu
process.

[YOCTO #12113]

(From OE-Core rev: 39ffa0f3779305c5e8ef86fe4572e961c5912021)

Signed-off-by: Leonardo Sandoval <leonardo.sandoval.gonzalez@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/utils/qemurunner.py

@@ -51,6 +51,7 @@ class QemuRunner:
         self.logged = False
         self.thread = None
         self.use_kvm = use_kvm
+        self.msg = ''
 
         self.runqemutime = 120
         self.qemu_pidfile = 'pidfile_'+str(os.getpid())
@@ -79,6 +80,7 @@ class QemuRunner:
             # because is possible to have control characters
             msg = msg.decode("utf-8", errors='ignore')
             msg = re_control_char.sub('', msg)
+            self.msg += msg
             with codecs.open(self.logfile, "a", encoding="utf-8") as f:
                 f.write("%s" % msg)
 
@@ -307,9 +309,12 @@ class QemuRunner:
                         sock.close()
                         stopread = True
 
+
         if not reachedlogin:
             self.logger.info("Target didn't reached login boot in %d seconds" % self.boottime)
-            lines = "\n".join(bootlog.splitlines()[-25:])
+            tail = lambda l: "\n".join(l.splitlines()[-25:])
+            # in case bootlog is empty, use tail qemu log store at self.msg
+            lines = tail(bootlog if bootlog else self.msg)
             self.logger.info("Last 25 lines of text:\n%s" % lines)
             self.logger.info("Check full boot log: %s" % self.logfile)
             self._dump_host()