Ignore IOError from missing child.log.

Summary:
TestMiCliSupport (among other TestMi*) fails on Linux with

```
IOError: [Errno 2] No such file or directory: 'child.log'
```

Reviewers: clayborg, ki.stfu

Reviewed By: ki.stfu

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D8843

llvm-svn: 234191

lldb/test/tools/lldb-mi/lldbmi_testcase.py

@@ -25,7 +25,10 @@ class MiTestCaseBase(Base):
     def tearDown(self):
         if self.TraceOn():
             print "\n\nContents of %s:" % self.mylog
-            print open(self.mylog, "r").read()
+            try:
+                print open(self.mylog, "r").read()
+            except IOError:
+                pass
         Base.tearDown(self)
 
     def spawnLldbMi(self, args=None):