Fixed pip with http(s)_proxy

pip failed to insall packages with the http_proxy and https_proxy localrc
environment variables. indeed, the case of the variables was uppercase
and these variables are normally lowercase.

Change-Id: I73054aafd353ccf53986f0ec05426f6a2c4e2240
Closes-Bug: 1307492
Rename ironic option drivers_whitelist -> enabled_drivers

There were competing patches to implement this feature in Ironic.

Patch I2da37409cea98731a2ca18dfe7298861fde37783 calls the option
'enabled_drivers', which is more consistent with other option names.

Change-Id: Ifa7eae594c6d9ea743a17b4c31e407501bba8467
Merge "Fixed pip with http(s)_proxy"
Merge "Rename ironic option drivers_whitelist -> enabled_drivers"
Merge branch 'master' of github.com:openstack-dev/devstack