RFC V2 [0/2] test-in-container

[DJ Delorie <dj at redhat dot com>]

Second version of this patch.  This includes changes need to combine
test-in-container with cross-test-ssh, tested with a riscv/fedora remote
system, as well as native.

Note that the setup rules use $(test-wrapper) a lot, as well as running
the just-built ld-linux-*.so, to set up the container on the target
where needed.  This assumes that your test system and the cross compiler
have compatible ABIs and installed .so's.  If not, well, I don't know
what you're planning on testing that would still work at all ;-)

Also, a simple lock was added to support "make -j" but it does so by
preventing container'd tests from running in parallel.

The first patch [1/2] contains the infrastructure, mostly in
support/test-container.c which maintains the test-specific container
and manages the containerization.

The second patch [2/2] shows how to migrate a test to this system, by
migrating nss/tst-nss-test3.


For reference...
V1 0/2: https://www.sourceware.org/ml/libc-alpha/2018-02/msg00302.html
V1 1/2: https://www.sourceware.org/ml/libc-alpha/2018-02/msg00303.html
V1 2/2: https://www.sourceware.org/ml/libc-alpha/2018-02/msg00304.html