oe-buildenv-internal: Add upper and lower case proxy vars to BB_ENV_EXTRAWHITE

oe-buildenv-internal: Add upper and lower case proxy vars to BB_ENV_EXTRAWHITE

Applications are inconsistent in their use of upper and lower case proxy
variables. Curl, for example, specifies NO_PROXY (not no_proxy) in the
man page (changed in 2009 [1]). Avoid proxy issues by ensuring both the
upper and lower case versions of each proxy variable are available in
the environment for the fetcher commands.

Add FTPS_PROXY and ftps_proxy to the list as well.

1. http://curl.haxx.se/mail/tracker-2009-04/0012.html

(From OE-Core rev: 684c6512850ceb108e52af634be98eaacb8351e1)

Signed-off-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>