[SPARK-9136] [SQL] fix several bugs in DateTimeUtils.stringToTimestamp

a follow up of https://github.com/apache/spark/pull/7353

1. we should use `Calendar.HOUR_OF_DAY` instead of `Calendar.HOUR`(this is for AM, PM).
2. we should call `c.set(Calendar.MILLISECOND, 0)` after `Calendar.getInstance`

I'm not sure why the tests didn't fail in jenkins, but I ran latest spark master branch locally and `DateTimeUtilsSuite` failed.

Author: Wenchen Fan <cloud0fan@outlook.com>

Closes #7473 from cloud-fan/datetime and squashes the following commits:

66cdaf2 [Wenchen Fan] fix several bugs in DateTimeUtils.stringToTimestamp

2 files changed, 14 insertions, 4 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala
index 53c32a0a98..f33e34b380 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala
@@ -320,16 +320,17 @@ object DateTimeUtils {
       Calendar.getInstance(
         TimeZone.getTimeZone(f"GMT${timeZone.get.toChar}${segments(7)}%02d:${segments(8)}%02d"))
     }
+    c.set(Calendar.MILLISECOND, 0)
 
     if (justTime) {
-      c.set(Calendar.HOUR, segments(3))
+      c.set(Calendar.HOUR_OF_DAY, segments(3))
       c.set(Calendar.MINUTE, segments(4))
       c.set(Calendar.SECOND, segments(5))
     } else {
       c.set(segments(0), segments(1) - 1, segments(2), segments(3), segments(4), segments(5))
     }
 
-    Some(c.getTimeInMillis / 1000 * 1000000 + segments(6))
+    Some(c.getTimeInMillis * 1000 + segments(6))
   }
 
   /**
diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/util/DateTimeUtilsSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/util/DateTimeUtilsSuite.scala
index c65fcbc4d1..5c3a621c6d 100644
--- a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/util/DateTimeUtilsSuite.scala
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/util/DateTimeUtilsSuite.scala
@@ -243,8 +243,17 @@ class DateTimeUtilsSuite extends SparkFunSuite {
       UTF8String.fromString("2015-03-18T12:03:17.12312+7:30")).get ===
         c.getTimeInMillis * 1000 + 120)
 
+    c = Calendar.getInstance()
+    c.set(Calendar.HOUR_OF_DAY, 18)
+    c.set(Calendar.MINUTE, 12)
+    c.set(Calendar.SECOND, 15)
+    c.set(Calendar.MILLISECOND, 0)
+    assert(DateTimeUtils.stringToTimestamp(
+      UTF8String.fromString("18:12:15")).get ===
+      c.getTimeInMillis * 1000)
+
     c = Calendar.getInstance(TimeZone.getTimeZone("GMT+07:30"))
-    c.set(Calendar.HOUR, 18)
+    c.set(Calendar.HOUR_OF_DAY, 18)
     c.set(Calendar.MINUTE, 12)
     c.set(Calendar.SECOND, 15)
     c.set(Calendar.MILLISECOND, 123)
@@ -253,7 +262,7 @@ class DateTimeUtilsSuite extends SparkFunSuite {
       c.getTimeInMillis * 1000 + 120)
 
     c = Calendar.getInstance(TimeZone.getTimeZone("GMT+07:30"))
-    c.set(Calendar.HOUR, 18)
+    c.set(Calendar.HOUR_OF_DAY, 18)
     c.set(Calendar.MINUTE, 12)
     c.set(Calendar.SECOND, 15)
     c.set(Calendar.MILLISECOND, 123)