Add upstream autopkgtest to run installed test binaries (Closes: #1053333)

The existing smoke test is superficial and doesn't exercise core functionality. Rebuilding in autopkgtest to run upstream tests is discouraged as it's redundant with the build process and wastes resources.

Add a new 'upstream' autopkgtest that runs test binaries from a galera-test package instead. This follows Debian best practices by testing the installed package rather than rebuilding it.

NOTE: As this introduces a new binary package galera-test and passing the NEW queue has in past year taken on average 2-6 months for my uploads, I am intentionally postponing merging and uploading this until a time when I am confident no other Galera uploads or fixes are needed and the package can sit dormant for 6 months without issues.