Rollback of commit 8bb4299.

*** Reason for rollback ***

Suspected root cause for Windows bootstrap on Bazel CI breakage:

java.lang.NullPointerException
	at com.google.devtools.build.lib.vfs.Path$1.run(Path.java:123)

http://ci.bazel.io/view/Bazel%20bootstrap%20and%20maintenance/job/Bazel/922/JAVA_VERSION=1.8,PLATFORM_NAME=windows-x86_64/console

*** Original change description ***

VFS, WindowsFileSystem: fix UNIX_ROOT retrieval

Executing bash.exe directly instead of through
cmd.exe doesn't seem to work. This change fixes
that problem.

Fixes bazelbuild#1463 (again)

--
MOS_MIGRATED_REVID=136581532

src/main/java/com/google/devtools/build/lib/vfs/WindowsFileSystem.java

@@ -20,7 +20,6 @@
 import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.IOException;
-import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.nio.file.Files;
 import java.nio.file.LinkOption;
@@ -171,11 +170,9 @@ private static WindowsPath translateParent(WindowsPath parent, String name) {
             UNIX_ROOT,
             "Could not determine Unix path root or it is not an absolute Windows path. Set the "
                 + "\"%s\" JVM argument, or export the \"%s\" environment variable for the MSYS bash"
-                + " and have /usr/bin/cygpath installed. Parent is \"%s\", name is \"%s\".",
+                + " and have /usr/bin/cygpath installed",
             WINDOWS_UNIX_ROOT_JVM_ARG,
-            BAZEL_SH_ENV_VAR,
-            parent,
-            name);
+            BAZEL_SH_ENV_VAR);
 
         return (WindowsPath) parent.getRelative(UNIX_ROOT);
       } else {
@@ -411,19 +408,19 @@ private static PathFragment determineUnixRoot(String jvmArgName, String bazelShE
       String bash = System.getenv(bazelShEnvVar);
       Process process = null;
       try {
-        process = Runtime.getRuntime().exec("cmd.exe /C " + bash + " -c \"/usr/bin/cygpath -m /\"");
+        process = Runtime.getRuntime().exec(bash + "-c \"/usr/bin/cygpath -m /\"");
 
         // Wait 3 seconds max, that should be enough to run this command.
         process.waitFor(3, TimeUnit.SECONDS);
 
         if (process.exitValue() == 0) {
-          path = readAll(process.getInputStream());
-        } else {
-          System.err.print(
-              String.format(
-                  "ERROR: %s (exit code: %d)%n",
-                  readAll(process.getErrorStream()),
-                  process.exitValue()));
+          char[] buf = new char[256];
+          try (InputStreamReader r = new InputStreamReader(process.getInputStream())) {
+            int len = 0;
+            while ((len = r.read(buf)) > 0) {
+              path = path + new String(buf, 0, len);
+            }
+          }
         }
       } catch (InterruptedException | IOException e) {
         // Silently ignore failure. Either MSYS is installed at a different location, or not
@@ -440,18 +437,4 @@ private static PathFragment determineUnixRoot(String jvmArgName, String bazelShE
       return result;
     }
   }
-
-  private static String readAll(InputStream s) {
-    String result = "";
-    int len;
-    char[] buf = new char[4096];
-    try (InputStreamReader r = new InputStreamReader(s)) {
-      while ((len = r.read(buf)) > 0) {
-        result += new String(buf, 0, len);
-      }
-    } catch (IOException e) {
-      return null;
-    }
-    return result;
-  }
 }