oe-setup-builddir: substitute ##OEROOT## when using templates

oe-setup-builddir: substitute ##OEROOT## when using templates

oe-setup-builddir substitutes ##COREBASE## which seems like it should have the
same value as the variable ${COREBASE}.  In reality it doesn't as ##COREBASE##
is substituted with the value of $OEROOT (the location of the oe-init-build-env
script), whereas ${COREBASE} is set by oe-core to the parent directory of meta/.
If oe-core's meta/ isn't a top-level directory then ##COREBASE## and ${COREBASE}
have different values, which can lead to confusion.

To resolve this, deprecate (but still substitute) ##COREBASE## and substitute
 ##OEROOT# for $OEROOT.

(From OE-Core rev: 1890783928dd1c73105fae32fb6c588afc287ff6)

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>