sanity.bbclass: when bblayers.conf is updated, it invokes a reparse

sanity.bbclass: when bblayers.conf is updated, it invokes a reparse

When bblayers.conf is updated(when sanity check is running), it should
tell to bitbake to reparse configuration files. I will send a patch to
bitbake-devel, with the actions needed in bitbake and hob.

[YOCTO #3213]
(From OE-Core rev: 5db1ff93f7204b43b7242fc7ef415216eb632ed8)

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