test-container: Avoid copying unintended system libraries

Some DSOs are distributed in hardware capability directories, e.g.
/usr/lib64/power7/libc.so.6
Whenever the processor is able to use one of these hardware-enabled
DSOs, testroot.pristine ends up with copies of glibc-provided libraries
from the system because it can't overwrite or remove them.

This patch avoids the unintended copies by executing ld.so with the same
arguments passed to each glibc test.

	* Makefile (testroot.pristine/install.stamp): Execute ld.so with
	the same arguments used in all tests.