test-container: Install with $(all-subdirs) [BZ #24794]
Whenever a sub-make is created, it inherits the variable subdirs from its
parent. This is also true when make check is called with a restricted
list of subdirs. In this scenario, make install is executed "partially"
and testroot.pristine ends up with an incomplete installation.
[BZ #24794]
* Makefile (testroot.pristine/install.stamp): Pass
subdirs='$(all-subdirs)' to make install.