The reason for this is to fix the automatic rebuild of libvirt-common.h.in.
All *.in files should be automatically rebuilt each time they're modified.
It works well for makefiles and pkgconfig files, since they do have a valid
dependency in the top-level Makefile. However, with libvirt-common.h.in
there is no dependency in the top-level Makefile and there's no need for it
either, so this rule

include/libvirt/libvirt-common.h: $(top_builddir)/config.status \
        $(top_srcdir)/include/libvirt/libvirt-common.h.in
    cd $(top_builddir) && $(SHELL) ./config.status $@

is never hit and should be moved to include/Makefile, but that's automake's
job. According to GNU automake docs:

"Files created by AC_CONFIG_FILES, be they
Automake Makefiles or not, are all removed by ‘make distclean’. Their inputs
are automatically distributed, unless they are the output of prior
AC_CONFIG_FILES commands. Finally, rebuild rules are generated in the Automake
Makefile existing in the subdirectory of the output file, if there is one, or
in the top-level Makefile otherwise."

Which means that if we want to have the rule for libvirt-common.h automatically
generated by automake, the include/Makefile.am needs to be moved into libvirt/
subdirectory and $SUBDIRS in the top-level Makefile need to be adjusted as
well. This patch moves Makefile.am from include/ to include/libvirt, adjusting
the prefixes accordingly as well as updates the top-level Makefile $SUBDIRS to
properly hint automake to generate all rules at proper places.

Best way to see the changes, use -M with 'git show'.
Signed-off-by: NErik Skultety <eskultet@redhat.com>