Python from host fails when not installed under /usr

[johannesring]

[python] Building python/qlvjlzdbishm, follow log with:
[python]   tail -f /cluster/home/johannr/.hashdist/tmp/python-qlvjlzdbishm-1/_hashdist/build.log
[python] running [u'/bin/bash', '_hashdist/build.sh']
[python] environment:
[python]   {'ARTIFACT': u'/cluster/home/johannr/.hashdist/bld/python/qlvjlzdbishm',
[python]    'BASH': u'/bin/bash',
[python]    'BUILD': u'/cluster/home/johannr/.hashdist/tmp/python-qlvjlzdbishm-1',
[python]    'HASHDIST_CPU_COUNT': '1',
[python]    'HDIST_CONFIG': '{"gc_roots":"/cluster/home/johannr/.hashdist/gcroots","build_stores":[{"dir":"/cluster/home/johannr/.hashdist/bld"}],"source_caches":[{"dir":"/cluster/home/johannr/.hashdist/src"}],"cache":"/cluster/home/johannr/.hashdist/cache","build_temp":"/cluster/home/johannr/.hashdist/tmp"}',
[python]    'HDIST_IMPORT': '',
[python]    'HDIST_IMPORT_PATHS': '',
[python]    'HDIST_VIRTUALS': '',
[python]    'PATH': u'/usr/bin:/bin',
[python]    'PWD': u'/cluster/home/johannr/.hashdist/tmp/python-qlvjlzdbishm-1'}
[python] cp: cannot stat `/usr/bin/python2.7': No such file or directory
[python|ERROR] Command '[u'/bin/bash', '_hashdist/build.sh']' returned non-zero exit status 1
[python|ERROR] command failed (code=1); raising

I will prepare a pull request.