Travis: running more tests for cache component

- enabled `Apc` storage adapter tests using last available `apcu` extension
- enabled `Memcache` storage adapter tests using pre-installed but not enabled `memcache` extension
- enabled `Memcached` storage adapter tests using pre-installed but not enabled `memcached` extension
  - start memcached on `before_script` 
- enabled `Redis` storage adapter tests using pre-installed but not enabled `redis` extension
  - start redis-server on `before_script` 
- enabled all other storage adapter tests even if they are not available.
  - the tests will be skipped automatically but this enables testing of the availability check + expected exception
- removed constant for SQLite because the is no Sqlite storage adapter yet

There are some tests failing currently but these should be solved by #7065 and #7043

@Ocramius ping