Merge branch 'rnou/173-support-other-kv-databases' into 'master'

Resolve "Support other KV Databases"

Closes #173

This `MR` adds support for different metadata backends. Actually, `PARALLAX` from `FORTH` is supported as experimental.
`PARALLAX` needs a 8GB file (minimum size) to store metadata. It is created in the `metadir` directory as `rocksdbx` name.
Inside the install script there is a commented line, to modify an internal parameter of `PARALLAX` increasing the key size drom 255 bytes to 4096 (Max PATH name in POSIX). However, `PARALLAX` is not (fully) tested with such values.

This backend should work in all the scenarios, but there are some issues that appear under high load mdtest.

This `MR` includes the optional compilation/dependencies of each of the backends. Testing is generated dynamically from conftest.template depending on the options selected.

This `MR` includes a new argument for the daemon to remove the rootdir/metadir files directories when the daemon is finished. This reduces the data from artifacts when running databases that uses a fixed size file. (i.e., Parallax)

See merge request !110