CLC-4638: fixes for My Finances Selenium tests

https://jira.ets.berkeley.edu/jira/browse/CLC-4638

Changes:
* Remove "API sanity tests" that checked for consistency in the dollar amounts coming from the financials API.  The QA instance of CFV frequently returns inconsistent values, but the problem is not reproducible in Prod CFV.  The tests are therefore more vexing than helpful.
* Fixed the link-checking tests in the My Finances landing page spec to use a util for checking external links, which removes a load of redundant Selenium code.  Also fixed the handling of browser alerts in the util.
* Cleaned up the code a wee bit, and added a test to verify that at least some test UIDs have financials data.