avocado/utis/process.py: fix GDB commands file with non-absolute path

The path of the binary that is fed into the GDB commands file can be
a relative path, which can cause the behavior described in issue #412.

CC: Lukáš Doktor <ldoktor@redhat.com>
Signed-off-by: NCleber Rosa <crosa@redhat.com>

avocado/utils/process.py

@@ -576,7 +576,7 @@ class GDBSubProcess(object):
             script_name = '%s.gdb.connect_commands' % binary_name
             path = os.path.join(current_test.outputdir, script_name)
             cmds = open(path, 'w')
-            cmds.write('file %s\n' % self.binary)
+            cmds.write('file %s\n' % os.path.abspath(self.binary))
             cmds.write('target extended-remote :%s\n' % self.gdb_server.port)
             cmds.close()
             return path