Move find_bitbake_env_line() since they're going to need to be
accessible from source plugins.
(From OE-Core rev: d881ec6136255fd0f4a8cf36f9ce148ade02c103)
Signed-off-by: João Henrique Ferreira de Freitas <joaohf@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>