Most of our code base uses space after comma but not before;
fix the remaining uses before adding a syntax check.

* src/conf/capabilities.c: Consistently use commas.
* src/conf/domain_conf.c: Likewise.
* src/conf/network_conf.c: Likewise.
* src/conf/storage_conf.c: Likewise.
Signed-off-by: NEric Blake <eblake@redhat.com>