phase1: use Interpolate instead of WithProperties

phase1: use Interpolate instead of WithProperties

WithProperties is marked as deprecated since buildbot 0.8.7.

Trying to make the config future-proof, this patch replaces every
instance of WithProperties() by the corresponding Interpolate()
equivalent.

As of buildbot 0.8.9 it appears that Interpolate() doesn't correctly
handle integer format with parameters that call a function, so make
GetNumJobs() return a string:

  File "phase1/master.cfg", line 672, in <module>
    command = ["make", Interpolate("-j%(kw:jobs)d", jobs=GetNumJobs), "tools/tar/compile", "V=s"],
    fmtstring % dd
exceptions.TypeError: %d format: a number is required, not str
Configuration Errors:
  error while parsing config file: %d format: a number is required, not str (traceback in logfile)

Signed-off-by: Thibaut VARÈNE <hacks@slashdirt.org>