test: linting for buffer-free-callback test
test: linting for buffer-free-callback test

Test added in d1f24044 does not pass linting rule added in 3de353b5.
Fixed in this commit. `common` module required in all tests except
those that intentionally leak variables.

PR-URL: https://github.com/nodejs/node/pull/3230
Fixes: https://github.com/nodejs/node/issues/3229
Reviewed-By: Fedor Indutny <2e687df1861dff46b1954016c7b2cad32e8742d4@gmail.com>
Reviewed-By: Jeremiah Senkpiel <f1782d15e31ad502ea2c097c21cc235811d0cb7c@rocketmail.com>

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node