specify database for pg_terminate_backend

[stevenchanin]

The psql -c \"#{terminate_connection_sql};\" was running without a database specified. Postgres attempts to handle this by connecting to a database with the same name as the current user. If you don't have a database with that name, you get an error:

      executing local: bunzip2 -f db/xyz_production_2016-08-19-121802.sql.bz2 &&  psql -c "SELECT pg_terminate_backend(pg_stat_activity.pid) FROM pg_stat_activity WHERE pg_stat_activity.datname = 'xyz_development' AND pid <> pg_backend_pid();;" ;  dropdb  xyz_development;  createdb  xyz_development;  psql  -d xyz_development < db/xyz_production_201…

psql: FATAL:  database "steven" does not exist

This change supplies the name of a valid database so the terminate_backend command will run without error.

      executing local: bunzip2 -f db/xyz_production_2016-08-19-122005.sql.bz2 &&  psql -c "SELECT pg_terminate_backend(pg_stat_activity.pid) FROM pg_stat_activity WHERE pg_stat_activity.datname = 'xyz_development' AND pid <> pg_backend_pid();;"  xyz_development;  dropdb  xyz_development;  createdb  xyz_development;  psql  -d xyz_development < db/di…
 pg_terminate_backend
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(0 rows)

Closes #84

[numbata]

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