master-qa-6335

https://issues.liferay.com/browse/LIFERAYQA-6335

This is for the db upgrade testing.

There are 3 main things that I did.

1. I changed all the "sql.version" variables to "portal.version" to match what's in liferay-qa-portal-ee. I think that "portal.version" is better than "sql.version" anyways because "sql.version" seems more likely to mean MySQL or Oracle version rather than the Liferay Portal version. I also edited prepare-portal-ext to include the legacy properties for 6.1 (I didn't do this in the 6.1 pulls). 

2. I removed a section of build-test-plugins that deletes the home folder. There is already a target that is run earlier that clears out the home folder. This particular one will actually delete the legacy data folder after it gets unzipped.

3. I added "rebuild-legacy-database".
This unzips the data-archive.zip and imports legacy database.

Right now the way I have it, we need to point it to the legacy repo locally. Ideally we would download the data-archive.zip directly, but there isn't a simple way of doing it from github because github will append a token to the URL's.

Let me know if there are things you'd want me to change.