Check the account existence before executing to set the default account
to improve the test's reliability

Bug: 422309768
Flag: EXEMPTED
Test: atest android.provider.cts.contacts.ContactsContract_MoveToCloudDeviceContactsAccount

Occasionally, the account may not be added to the device or at least not
shown from AccountManager#getAccounts, which will fail the
setDefaultAccountForNewContacts and thus fail the test.

	modified:   tests/contactsprovider/src/android/provider/cts/contacts/ContactsContract_MoveToCloudDeviceContactsAccount.java

Change-Id: Ide35513766339c11b363e146f92629a96b846ff7