tdb: Fix compatibility of wscript with older python

tdb: Fix compatibility of wscript with older python

Traceback (most recent call last):
  File "tdb-1.3.17/third_party/waf/waflib/Scripting.py", line 158, in waf_entry_point
    run_commands()
  File "tdb-1.3.17/third_party/waf/waflib/Scripting.py", line 251, in run_commands
    ctx = run_command(cmd_name)
  File "tdb-1.3.17/third_party/waf/waflib/Scripting.py", line 235, in run_command
    ctx.execute()
  File "tdb-1.3.17/third_party/waf/waflib/Context.py", line 204, in execute
    self.recurse([os.path.dirname(g_module.root_path)])
  File "tdb-1.3.17/third_party/waf/waflib/Context.py", line 286, in recurse
    user_function(self)
  File "tdb-1.3.17/wscript", line 225, in testonly
    cmd = "BINDIR={} {}".format(blddir, sh_test)
ValueError: zero length field name in format

Signed-off-by: Lukas Slebodnik <lslebodn@fedoraproject.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Sun Jan 20 03:49:59 CET 2019 on sn-devel-144

(cherry picked from commit 0628ca2a558871402f9a17cc7f7a0c69d857ae19)