If a python recipe is using setuptools and the setup_requires argument, where
setuptools will use easy_install to fetch the module if it isn't
present.

The build failed on a machine where a proxy was required, but succeeded on a
machine which had direct access to the internet

Add var-NO_FETCH_BUILD, and set it in distutils_do_compile which does not
allow to fetch code from internet during do_compile.

Example result:
...
ERROR: Do not try to fetch `pytest-runner1' for building. Please add its native recipe to DEPENDS.
Traceback (most recent call last):
  File "setup.py", line 56, in <module>
...

The improvement is flexible for test_requirements argument (used at
`setup.py test'), where use easy_install also.

[YOCTO #12084]
Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>