fix missing import of 'time' in lldbutil.wait_for_file_on_target

This triggers in some timeout scenarios in the LLDB test suite.

Fixes:
https://bugs.swift.org/browse/SR-1193

llvm-svn: 265821
diff --git a/lldb/packages/Python/lldbsuite/test/lldbutil.py b/lldb/packages/Python/lldbsuite/test/lldbutil.py
index bf17006..021ae2d 100644
--- a/lldb/packages/Python/lldbsuite/test/lldbutil.py
+++ b/lldb/packages/Python/lldbsuite/test/lldbutil.py
@@ -1038,6 +1038,7 @@
             break
         if i < max_attempts:
             # Exponential backoff!
+            import time
             time.sleep(pow(2, i) * 0.25)
     else:
         testcase.fail("File %s not found even after %d attempts." % (file_path, max_attempts))