Pass --isolated to pip (#232)

This fixes an issue where if you have bad URLs in your ~/.pip/pip.conf,
pip would pick them up and end up failing bazel. This way we make
pip_import more hermetic and ignore user config.

packaging/piptool.py

diff --git a/packaging/piptool.py b/packaging/piptool.py
index 838ba42..2544032 100644
--- a/packaging/piptool.py
+++ b/packaging/piptool.py
@@ -78,7 +78,7 @@
     atexit.register(lambda: shutil.rmtree(cert_tmpdir, ignore_errors=True))
     with open(cert_path, "wb") as cert:
       cert.write(pkgutil.get_data("pip._vendor.requests", "cacert.pem"))
-    argv = ["--disable-pip-version-check", "--cert", cert_path] + argv
+    argv = ["--isolated", "--disable-pip-version-check", "--cert", cert_path] + argv
     return pip.main(argv)
 
 from packaging.whl import Wheel

tools/piptool.par

diff --git a/tools/piptool.par b/tools/piptool.par
index 6f71bb6..f0e0f22 100755
--- a/tools/piptool.par
+++ b/tools/piptool.par
Binary files differ