Change dump (with clean flag) and import method for psql

[dfang]

for postgres database, i changed dump with clean flag then import.

normally, we use cap staging db:pull or db:push to sync databases between local and staging for testing, i think this is enough, we don't need to terminate the conection(there is a syntax problem about this, see this issue #28), dropdb, createdb then import

what do you think ?

[sgruhier]

I'm not a postgres user.
I'm ok to merge that PR, anyone to confirm we can remove the terminate command? Or may add it as an option?

[rafaelsales]

@sgruhier I've been doing manually the process this gem does and I never terminate server process on a database. In many projects I worked on, it's common that developers copy production database to their local machines.

I don't think disturbing the production users is a good idea. Moreover, I never faced issues with production dumps even when the site is in reasonable traffic.

I'm confident this is good to go.