Improve fastboot verbose output.

Move some verbose messages so they're only output with -v.

Remove some misleading verbose messages altogether (such as "wiping
userdata...").

Properly log all the commands sent and responses received. Example:

  $ fastboot -v flashall
  ...
  Sending sparse 'system' 2/2 (443712 KB)
  fastboot: verbose: sending command "download:1b1500d0"
  fastboot: verbose: received DATA 1b1500d0
  fastboot: verbose: sending data (1024 bytes)
  fastboot: verbose: sending data (165596160 bytes)
  fastboot: verbose: sending data (1024 bytes)
  fastboot: verbose: sending data (267762688 bytes)
  fastboot: verbose: sending data (1024 bytes)
  fastboot: verbose: sending data (20978688 bytes)
  fastboot: verbose: sending data (1024 bytes)
  fastboot: verbose: sending data (7168 bytes)
  fastboot: verbose: sending data (1024 bytes)
  fastboot: verbose: sending data (3072 bytes)
  fastboot: verbose: sending data (1024 bytes)
  fastboot: verbose: sending data (3072 bytes)
  fastboot: verbose: sending data (1024 bytes)
  fastboot: verbose: sending data (3072 bytes)
  fastboot: verbose: sending data (208 bytes)
  fastboot: verbose: received OKAY
  OKAY [ 13.871s]
  Writing sparse 'system' 2/2
  fastboot: verbose: sending command "flash:system"
  fastboot: verbose: received OKAY
  OKAY [  3.228s]
  Rebooting
  fastboot: verbose: sending command "reboot"
  fastboot: verbose: received OKAY

  Finished. Total time: 36.939s

Bug: http://b/30953083
Bug: http://b/74444116
Test: `fastboot -v flashall`
Change-Id: I2cca198daa062fd1fb732218343263803b111e38
diff --git a/fastboot/util.cpp b/fastboot/util.cpp
index 53fc1be..140270f 100644
--- a/fastboot/util.cpp
+++ b/fastboot/util.cpp
@@ -35,6 +35,8 @@
 
 #include "fastboot.h"
 
+static bool g_verbose = false;
+
 double now() {
     struct timeval tv;
     gettimeofday(&tv, NULL);
@@ -46,11 +48,28 @@
     va_start(ap, fmt);
     fprintf(stderr, "fastboot: error: ");
     vfprintf(stderr, fmt, ap);
-    fprintf(stderr,"\n");
+    fprintf(stderr, "\n");
     va_end(ap);
     exit(EXIT_FAILURE);
 }
 
+void set_verbose() {
+    g_verbose = true;
+}
+
+void verbose(const char* fmt, ...) {
+    if (!g_verbose) return;
+
+    if (*fmt != '\n') {
+        va_list ap;
+        va_start(ap, fmt);
+        fprintf(stderr, "fastboot: verbose: ");
+        vfprintf(stderr, fmt, ap);
+        va_end(ap);
+    }
+    fprintf(stderr, "\n");
+}
+
 char* xstrdup(const char* s) {
     char* result = strdup(s);
     if (!result) die("out of memory");