bitbake: hob: changed the split of SSTATE_MIRRORS variable

bitbake: hob: changed the split of SSTATE_MIRRORS variable

Until now the split made searching the string "file://", but
this is not ok when SSTATE_VARIABLE has the following form:
SSTATE_MIRRORS ?= "\
     file://.* http://someserver.tld/share/sstate/PATH \n \
     file://.* file:///some/local/dir/sstate/PATH"

In the documentation I've found that \n is the list separator.

[YOCTO #4857]
(Bitbake rev: 73bcd96928cb2df390e1fc6d3a8b7ce3e9d546a4)

Signed-off-by: Cristiana Voicu <cristiana.voicu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>