detect the number of available CPU for plumed make, as suggested by @akohlmey

  os.remove("%s/%s" % (homepath,filename))

  # build plumed

if buildflag:

  print("Building plumed ...")

   cmd = 'cd %s/plumed-%s; ./configure --prefix=%s --enable-static-patch ; make -j8 ; make install' % (homepath,version,homedir)

  try:

    import multiprocessing

    n_cpus = multiprocessing.cpu_count()

  except:

    n_cpus = 1

  cmd = 'cd %s/plumed-%s; ./configure --prefix=%s --enable-static-patch ; make -j%d ; make install' % (homepath,version,homedir,n_cpus)

  txt = subprocess.check_output(cmd,stderr=subprocess.STDOUT,shell=True)

  print(txt.decode('UTF-8'))

# 

# create 2 links in lib/plumed to plumed2 installation dir

if linkflag: