do not use -all-root in mksquashfs (#213)

Author: simonpintarelli

stackinator/templates/Makefile

@@ -83,7 +83,7 @@ store.squashfs: post-install
 	# clean up the __pycache__ paths in the repo
 	$(SANDBOX) find $(STORE)/repo -type d -name __pycache__ -exec rm -r {} +
 	$(SANDBOX) chmod -R a+rX $(STORE)
-	$(SANDBOX) env -u SOURCE_DATE_EPOCH "$$($(SANDBOX) $(SPACK_HELPER) -e ./compilers/bootstrap find --format='{prefix}' squashfs | head -n1)/bin/mksquashfs" $(STORE) $@ -all-root -all-time $$(date +%s) -no-recovery -noappend -Xcompression-level 3
+	$(SANDBOX) env -u SOURCE_DATE_EPOCH "$$($(SANDBOX) $(SPACK_HELPER) -e ./compilers/bootstrap find --format='{prefix}' squashfs | head -n1)/bin/mksquashfs" $(STORE) $@ -force-uid nobody -force-gid nobody -all-time $$(date +%s) -no-recovery -noappend -Xcompression-level 3
 
 # Force push all built packages to the build cache
 cache-force: mirror-setup