Fix random test failure with make flags on test node

When running under testnode, there was sometimes this failure:

File "/srv/slapgrid/slappart8/srv/testnode/bee/inst/test0-0/parts/slapos.recipe.cmmi/slapos/recipe/cmmi/README.txt", line 521, in README.txt
Failed example:
    print(system(buildout))
Expected:
    Uninstalling package.
    Installing package.
    package: [ENV] CFLAGS = -I/sw/include
    package: [ENV] LDFLAGS = -L/sw/lib -L/some/extra/lib
    package: [ENV] TMP = /sample_buildout/parts/package/tmp
    package: Applying patches
    patching file configure
    patching file Makefile.dist
    patched-configure --prefix=/somewhere/else --with-threads --without-foobar
    building patched package
    installing patched package
    installing patched package-lib
    <BLANKLINE>
Got:
    Uninstalling package.
    Installing package.
    package: [ENV] CFLAGS = -I/sw/include
    package: [ENV] LDFLAGS = -L/sw/lib -L/some/extra/lib
    package: [ENV] TMP = /sample_buildout/parts/package/tmp
    package: Applying patches
    patching file configure
    patching file Makefile.dist
    patched-configure --prefix=/somewhere/else --with-threads --without-foobar
    building patched package
    installing patched package-lib
    installing patched package
    <BLANKLINE>

The order of in which installing patched package-lib and installing patched package are printed is not always same.

This test does make install install-lib with a Makefile containing:

all:
        @echo building package

install:
        @echo installing package

install-lib:
        @echo installing package-lib

@vpelletier and I investigated this and he pointed out that order of parts depends is not stable when make is invoked with -j option.

Turned out that on test node MAKEFLAGS is set to -j12.