Pip now supports retries on failure. If setting multiple pypi mirrors a
fallback will not occure until the failures have finished for the first
mirror. This can cause a substantial delay if mirror fallback occurs a
lot.
Change-Id: Iad37a9015a2d5c861a345a111bd1725b965a42d3
We have a good pattern of namespacing env vars with DIB_. Add support
for DIB_PYPI_MIRROR_URL* and maintain backwards compat support.
Change-Id: I434c9d1b14cd571b20754c9ad7cd64c936f8399a