avocado.core: Introduce job_id library

Separate the code that generates a job SHA1 on its own
library. It'll make things easier for unittesting and other
needs.
Signed-off-by: NLucas Meneghel Rodrigues <lmr@redhat.com>

avocado/core/job_id.py

+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+#
+# See LICENSE for more details.
+#
+# Copyright: Red Hat Inc. 2013-2014
+# Authors: Lucas Meneghel Rodrigues <lmr@redhat.com>
+
+import hashlib
+import random
+import socket
+import time
+
+_RAND_POOL = random.SystemRandom()
+_HOSTNAME = socket.gethostname()
+
+
+def get_job_id():
+    """
+    Create a job ID SHA1.
+
+    :return: SHA1 string
+    :rtype: str
+    """
+    info = '%s-%s-%s' % (_HOSTNAME,
+                         time.strftime('%Y-%m-%dT%H:%M:%S'),
+                         _RAND_POOL.getrandbits(64))
+    h = hashlib.sha1()
+    h.update(info)
+    return h.hexdigest()