The virSocketParse method was not doing any error reporting
which meant the true cause of the problem was lost. Remove
all error reporting from callers, and push it into virSocketParse

* src/util/network.c: Add error reporting to virSocketParse
* src/conf/domain_conf.c, src/conf/network_conf.c,
  src/network/bridge_driver.c: Remove error reporting in
  callers of virSocketParse