Remove explicit set of UPOWER_CONF_FILE_NAME in up-self-test.c;
instead the harness should set it.  In Guix we set it explicitly; the
right thing is to use AM_TEST_ENVIRONMENT and regenerate the
makefiles, but we can't regenerate because current autotools carp on
some things, so we patch the Makefile.in instead.

Also fix to not try to create /var/lib/upower if /var isn't writable.

Patch by Andy Wingo <wingo@igalia.com>
Reduced to upower 0.99.10 by Tobias Geerinckx-Rice <me@tobias.gr>

--- upower-0.99.2.orig/src/Makefile.in	2014-12-18 10:32:01.000000000 +0100
+++ upower-0.99.2/src/Makefile.in	2015-04-04 19:49:28.020843678 +0200
@@ -1789,7 +1790,7 @@
 @HAVE_SYSTEMDSYSTEMUNITDIR_TRUE@	@sed -e "s|\@libexecdir\@|$(libexecdir)|" $< > $@
 
 install-data-hook:
-	if test -w $(DESTDIR)$(prefix)/; then \
+	if test -w $(DESTDIR)$(localstatedir)/; then \
 		mkdir -p $(DESTDIR)$(historydir); \
 	fi