Allow extra flags when installing from requirement file

[arescope]

Could it be possible to specify in the virtualenv creation, when we specify the requirements some extra parameters for the pip command.

for example,
--allow-all-external
--allow-unverified
etc.

[ThiefMaster]

+1, that's very important since some packages require that. cx_oracle for example (that one needs an environment variable, too, by the way, in case that's not possible already)

[bradq]

👍 Running into the same issues this morning with argparse.