Refactoring CompanionAdTestCase.java

##Rationale
It was suggested by @BCjwhisenant that my next move be to refactor **CompanionAdTestCase.java**, as, while it did work correctly, it was a little clunky and difficult to read and as someone who is still a beginner, learning to refactor code is an important skill.

##Changed Files
**OnceUxUiAutomatorBase.java**
* Changed *msecToPreroll* to 8000 to allow for less fails when the video takes too long to load.

**CompanionAdTestCase.java**
* Consolidated *testCompanionAd* and *testCompanionAdVanish* into one test
  * moved asserts to utility methods waitForCompanionAdCheck and waitForEndOfAdCheck
  * changed name of *testCompanionAd* to *testCompanionAdPresence*
  * removed *testCompanionAdVanish*
* Removed if-else statements from utility methods
* Changed *waitForCompanionAdCheck* and *waitForEndOfAdCheck* from booleans to voids
* Updated javadoc comments
* removed extraneous imports