[SettingsProvider] fix connectivity test

TestOnly flag allows the test to read restricted @Readable setting
ALWAYS_ON_VPN_LOCKDOWN_WHITELIST.

BUG: 177239688
Test: atest com.android.server.ConnectivityServiceTest
Change-Id: If41708ad31de9cec3a102b4de4d237e96a448ef1
diff --git a/tests/common/AndroidTest_Coverage.xml b/tests/common/AndroidTest_Coverage.xml
index 7c8e710..7ad0863 100644
--- a/tests/common/AndroidTest_Coverage.xml
+++ b/tests/common/AndroidTest_Coverage.xml
@@ -14,7 +14,8 @@
 -->
 <configuration description="Runs coverage tests for Connectivity">
     <target_preparer class="com.android.tradefed.targetprep.TestAppInstallSetup">
-        <option name="test-file-name" value="ConnectivityCoverageTests.apk" />
+      <option name="test-file-name" value="ConnectivityCoverageTests.apk" />
+      <option name="install-arg" value="-t" />
     </target_preparer>
 
     <option name="test-tag" value="ConnectivityCoverageTests" />