glibc: ptest: Add running glibc time related test suite (Y2038) with ptest

This patch introduces new recipe - namely 'glibc-tests', which
builds and installs time related (to check if Y2038 support works) glibc
test suite to OE/Yocto built image.

It reuses code from already available 'glibc-testsuite' recipe,
which is run with 'bitbake glibc-testsuite -c check' and uses qemu
to execute remotely (via SSH) tests on some emulated machine.

This recipe installs time related glibc tests on some rootfs image.
Afterwards, those tests can be executed on the real hardware, to
facilitate validation of it with Y2038 problem compliance.

To test time related subset - one needs to call:
ptest-runner glibc-tests
then change the date after Y2038 threshold for 32 bit systems:
date -s "20 JAN 2038 18:00:00"
and then run ptest-runner again.

To facilitate debugging, source files are provided by default with
the unstripped debugging symbols. Such approach would reduce the
already complex recipe (as it inherits base glibc one), so there
is no need to also install *-dbg and *-src packages.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>