oeqa/parselogs: Don't use cwd for file transfers

If you run:

MACHINE=A bitbake <image> -c testimage
MACHINE=B bitbake <image> -c testimage

and A has errors in parselogs, machine B can pick these up and cause immense confusion. This is because the test transfers the log files to cwd which is usually TOPDIR. This is clearly bad and this patch uses a subdir of WORKDIR to ensure machines don't contaminate each other.

Also ensure any previous logs are cleaned up from any existing transfer directory.

index 98a959e..8238a77 100644
@@ -180,6 +180,9 @@ class ParseLogsTest(oeRuntimeTest):

     def getMachine(self):
         return oeRuntimeTest.tc.d.getVar("MACHINE", True)

+    def getWorkdir(self):
+        return oeRuntimeTest.tc.d.getVar("WORKDIR", True)
+
     #get some information on the CPU of the machine to display at the beginning of the output. This info might be useful in some cases. def getHardwareInfo(self):
         hwi = ""
@@ -217,16 +220,19 @@ class ParseLogsTest(oeRuntimeTest):

     #copy the log files to be parsed locally
     def transfer_logs(self, log_list):
-        target_logs = 'target_logs'
+        workdir = self.getWorkdir()
+        self.target_logs = workdir + '/' + 'target_logs'
+        target_logs = self.target_logs
         if not os.path.exists(target_logs):
             os.makedirs(target_logs)
+        bb.utils.remove(self.target_logs + "/*")
         for f in log_list:
             self.target.copy_from(f, target_logs)

     #get the local list of logs
     def get_local_log_list(self, log_locations):
         self.transfer_logs(self.getLogList(log_locations))
-        logs = [ os.path.join('target_logs',f) for f in os.listdir('target_logs') if os.path.isfile(os.path.join('target_logs',f)) ] +        logs = [ os.path.join(self.target_logs, f) for f in os.listdir(self.target_logs) if os.path.isfile(os.path.join(self.target_logs, f)) ] return logs

     #build the grep command to be used with filters and exclusions