Make the adjustment even if the test script is currently disabled. Consistently
use nyc to generate coverage with mocha even if the test script is currently
disabled.
This enables removing unnecessary `core/fs` dependencies which can be
replaced with `fs-extra`.
This commit also fixes a bug introduced in f868d1216d
where methods from `embark.fs` weren't available.
The reason for that is because we have several *Process instances
that are created through child process communication, specifically
process.send() APIs. Using those APIs, we can only send data structures
however, methods attached on any of those will get lost.
This is the case when sending embark.fs through process.send().
We still need fs in those places though, mostly because they are relying
on embarkPath and dappPath().
These places are now importing those functions from `embark-core`. Other
API such as writeFile or mkdirp() can be accessed through fs-extra
or fs modules.
