qemu: use line breaks in command line args written to log

The QEMU command line arguments are very long and currently all written
on a single line to /var/log/libvirt/qemu/$GUEST.log. This introduces
logic to add line breaks after every env variable and "-" optional
argument, and every positional argument. This will create a clearer log
file, which will in turn present better in bug reports when people cut +
paste from the log into a bug comment.

An example log file entry now looks like this:

  2018-12-14 12:57:03.677+0000: starting up libvirt version: 5.0.0, qemu version: 3.0.0qemu-3.0.0-1.fc29, kernel: 4.19.5-300.fc29.x86_64, hostname: localhost.localdomain
  LC_ALL=C \
  PATH=/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin \
  HOME=/home/berrange \
  USER=berrange \
  LOGNAME=berrange \
  QEMU_AUDIO_DRV=none \
  /usr/bin/qemu-system-ppc64 \
  -name guest=guest,debug-threads=on \
  -S \
  -object secret,id=masterKey0,format=raw,file=/home/berrange/.config/libvirt/qemu/lib/domain-33-guest/master-key.aes \
  -machine pseries-2.10,accel=tcg,usb=off,dump-guest-core=off \
  -m 1024 \
  -realtime mlock=off \
  -smp 1,sockets=1,cores=1,threads=1 \
  -uuid c8a74977-ab18-41d0-ae3b-4041c7fffbcd \
  -display none \
  -no-user-config \
  -nodefaults \
  -chardev socket,id=charmonitor,fd=23,server,nowait \
  -mon chardev=charmonitor,id=monitor,mode=control \
  -rtc base=utc \
  -no-shutdown \
  -boot strict=on \
  -device qemu-xhci,id=usb,bus=pci.0,addr=0x1 \
  -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x2 \
  -sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny \
  -msg timestamp=on
  2018-12-14 12:57:03.730+0000: shutting down, reason=failed

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

tests/commandtest.c

@@ -630,7 +630,7 @@ static int test16(const void *unused ATTRIBUTE_UNUSED)
     virCommandAddArg(cmd, "F");
     virCommandAddArg(cmd, "G  H");
 
-    if ((outactual = virCommandToString(cmd)) == NULL) {
+    if ((outactual = virCommandToString(cmd, false)) == NULL) {
         printf("Cannot convert to string: %s\n", virGetLastErrorMessage());
         goto cleanup;
     }
@@ -1135,6 +1135,67 @@ static int test25(const void *unused ATTRIBUTE_UNUSED)
 }
 
 
+/*
+ * Don't run program; rather, log what would be run.
+ */
+static int test26(const void *unused ATTRIBUTE_UNUSED)
+{
+    virCommandPtr cmd = virCommandNew("true");
+    char *outactual = NULL;
+    const char *outexpect =
+        "A=B \\\n"
+        "C='D  E' \\\n"
+        "true \\\n"
+        "--foo bar \\\n"
+        "--oooh \\\n"
+        "-f \\\n"
+        "--wizz 'eek eek' \\\n"
+        "-w \\\n"
+        "-z \\\n"
+        "-l \\\n"
+        "--mmm flash \\\n"
+        "bang \\\n"
+        "wallop";
+
+    int ret = -1;
+    int fd = -1;
+
+    virCommandAddEnvPair(cmd, "A", "B");
+    virCommandAddEnvPair(cmd, "C", "D  E");
+    virCommandAddArgList(cmd, "--foo", "bar", "--oooh", "-f",
+                         "--wizz", "eek eek", "-w", "-z", "-l",
+                         "--mmm", "flash", "bang", "wallop",
+                         NULL);
+
+    if ((outactual = virCommandToString(cmd, true)) == NULL) {
+        printf("Cannot convert to string: %s\n", virGetLastErrorMessage());
+        goto cleanup;
+    }
+    if ((fd = open(abs_builddir "/commandhelper.log",
+                   O_CREAT | O_TRUNC | O_WRONLY, 0600)) < 0) {
+        printf("Cannot open log file: %s\n", strerror(errno));
+        goto cleanup;
+    }
+    virCommandWriteArgLog(cmd, fd);
+    if (VIR_CLOSE(fd) < 0) {
+        printf("Cannot close log file: %s\n", strerror(errno));
+        goto cleanup;
+    }
+
+    if (STRNEQ(outactual, outexpect)) {
+        virTestDifference(stderr, outexpect, outactual);
+        goto cleanup;
+    }
+
+    ret = checkoutput("test26", NULL);
+
+ cleanup:
+    virCommandFree(cmd);
+    VIR_FORCE_CLOSE(fd);
+    VIR_FREE(outactual);
+    return ret;
+}
+
 static void virCommandThreadWorker(void *opaque)
 {
     virCommandTestDataPtr test = opaque;
@@ -1288,6 +1349,7 @@ mymain(void)
     DO_TEST(test23);
     DO_TEST(test24);
     DO_TEST(test25);
+    DO_TEST(test26);
 
     virMutexLock(&test->lock);
     if (test->running) {