qemu: Introduce qemuDomainHostdevPrivatePtr

Modeled after the qemuDomainDiskPrivatePtr logic, create a privateData
pointer in the _virDomainHostdevDef to allow storage of private data
for a hypervisor in order to at least temporarily store auth/secrets
data for usage during qemuBuildCommandLine.

NB: Since the qemu_parse_command (qemuParseCommandLine) code is not
expecting to restore the auth/secret data, there's no need to add
code to handle this new structure there.

Updated copyrights for modules touched. Some didn't have updates in a
couple years even though changes have been made.

Signed-off-by: John Ferlan <jferlan@redhat.com>

tests/virhostdevtest.c

@@ -1,5 +1,6 @@
 /*
  * Copyright (C) 2014 SUSE LINUX Products GmbH, Nuernberg, Germany.
+ * Copyright (C) 2014-2016 Red Hat, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -86,7 +87,7 @@ myInit(void)
 
     for (i = 0; i < nhostdevs; i++) {
         virDomainHostdevSubsys subsys;
-        hostdevs[i] = virDomainHostdevDefAlloc();
+        hostdevs[i] = virDomainHostdevDefAlloc(NULL);
         if (!hostdevs[i])
             goto cleanup;
         hostdevs[i]->mode = VIR_DOMAIN_HOSTDEV_MODE_SUBSYS;