Add locking to mutating fakeController methods
Add locking to mutating fakeController methods

The test for maas2Storage.RemoveAll was triggering a data race - the
goroutines for each parallel delete were clobbering each other's
filenames.

gabriel-samfira/juju,anastasiamac/juju,mjs/juju,bac/juju,bz2/juju,axw/juju,macgreagoir/juju,ericsnowcurrently/juju,dimitern/juju,waigani/juju,anastasiamac/juju,AdamIsrael/juju,mjs/juju,macgreagoir/juju,gabriel-samfira/juju,AdamIsrael/juju,makyo/juju,dimitern/juju,marcmolla/juju,dooferlad/juju,makyo/juju,makyo/juju,frankban/juju,axw/juju,perrito666/juju,gabriel-samfira/juju,anastasiamac/juju,anastasiamac/juju,alesstimec/juju,mikemccracken/juju,alesstimec/juju,bogdanteleaga/juju,dimitern/juju,axw/juju,mikemccracken/juju,mjs/juju,dimitern/juju,waigani/juju,mjs/juju,bac/juju,AdamIsrael/juju,reedobrien/juju,marcmolla/juju,marcmolla/juju,dooferlad/juju,frankban/juju,waigani/juju,kat-co/juju,macgreagoir/juju,axw/juju,macgreagoir/juju,ericsnowcurrently/juju,perrito666/juju,dooferlad/juju,alesstimec/juju,frankban/juju,mikemccracken/juju,gabriel-samfira/juju,perrito666/juju,anastasiamac/juju,howbazaar/juju,marcmolla/juju,waigani/juju,ericsnowcurrently/juju,reedobrien/juju,bogdanteleaga/juju,bogdanteleaga/juju,dooferlad/juju,axw/juju,reedobrien/juju,howbazaar/juju,howbazaar/juju,kat-co/juju,mjs/juju,bac/juju,kat-co/juju,howbazaar/juju,bz2/juju,perrito666/juju,bz2/juju,dooferlad/juju,bac/juju,kat-co/juju,bz2/juju,mjs/juju,gabriel-samfira/juju,mjs/juju,perrito666/juju,makyo/juju,reedobrien/juju,mikemccracken/juju,dimitern/juju,alesstimec/juju,alesstimec/juju,ericsnowcurrently/juju,frankban/juju,reedobrien/juju,mikemccracken/juju,howbazaar/juju,macgreagoir/juju,ericsnowcurrently/juju,bac/juju,frankban/juju,bogdanteleaga/juju,marcmolla/juju,bz2/juju,kat-co/juju,AdamIsrael/juju