Build target-side Thermal test with coverage.

Instrument Thermal test with coverage so that coverage can be collected
on Thermal implementation.

Test: make vts
Change-Id: I01e4bdf42351034d5fa0a0ff32848f33e0db3980
diff --git a/thermal/1.0/vts/functional/Android.bp b/thermal/1.0/vts/functional/Android.bp
index fedb760..bef7bc2 100644
--- a/thermal/1.0/vts/functional/Android.bp
+++ b/thermal/1.0/vts/functional/Android.bp
@@ -31,8 +31,12 @@
     ],
     static_libs: ["libgtest"],
     cflags: [
+        "--coverage",
         "-O0",
         "-g",
     ],
+    ldflags: [
+        "--coverage"
+    ]
 }