Fix result does not get correct locale tag.

 - phone.getContext return a null in Cuttle fish ROM. It make the test
   result get failed. Hence mock the Context instance to avoid this
   situation.

Bug: b/254731907
Test: atest passed.
Test: Manual test passed. After FDR, check Wellcome page in SUW show
correct locale with zh-TW sim.

Change-Id: I831c425116b15814197944dc58588ec76d0c1b3a
2 files changed