Optimize "open" method with context manager

Use opening context manager to open a file.
Change-Id: Ice9be6350fd01cbf5eec686ac68d7fc8b5a4d5bd
diff --git a/tools/skip_tracker.py b/tools/skip_tracker.py
index a47e217..b554514 100755
--- a/tools/skip_tracker.py
+++ b/tools/skip_tracker.py
@@ -73,21 +73,23 @@
     DEF_RE = re.compile(r'\s*def (\w+)\(')
     bug_found = False
     results = []
-    lines = open(path, 'rb').readlines()
-    for x, line in enumerate(lines):
-        if not bug_found:
-            res = BUG_RE.match(line)
-            if res:
-                bug_no = int(res.group(1))
-                debug("Found bug skip %s on line %d", bug_no, x + 1)
-                bug_found = True
-        else:
-            res = DEF_RE.match(line)
-            if res:
-                method = res.group(1)
-                debug("Found test method %s skips for bug %d", method, bug_no)
-                results.append((method, bug_no))
-                bug_found = False
+    with open(path, 'rb') as content:
+        lines = content.readlines()
+        for x, line in enumerate(lines):
+            if not bug_found:
+                res = BUG_RE.match(line)
+                if res:
+                    bug_no = int(res.group(1))
+                    debug("Found bug skip %s on line %d", bug_no, x + 1)
+                    bug_found = True
+            else:
+                res = DEF_RE.match(line)
+                if res:
+                    method = res.group(1)
+                    debug("Found test method %s skips for bug %d",
+                          method, bug_no)
+                    results.append((method, bug_no))
+                    bug_found = False
     return results