Optimize regular expression for postgres config parsing

[chris-rock]

This PR optimizes the configuration parsing for PostgreSQL. Assuming we have the following configuration:

root@default-apt-ubuntu-1404:~# cat /etc/postgresql/9.4/main/postgresql.conf
# PostgreSQL configuration file
# This file was automatically generated and dropped off by chef!
# Please refer to the PostgreSQL documentation for details on
# configuration settings.

data_directory = '/var/lib/postgresql/9.4/main'
datestyle = 'iso, mdy'
default_text_search_config = 'pg_catalog.english'
external_pid_file = '/var/run/postgresql/9.4-main.pid'
hba_file = '/etc/postgresql/9.4/main/pg_hba.conf'
ident_file = '/etc/postgresql/9.4/main/pg_ident.conf'
listen_addresses = 'localhost'
log_connections = on
log_directory = 'pg_log'
log_disconnections = on
log_duration = on
log_hostname = on
log_line_prefix = '%t %u %d %h'
logging_collector = on
max_connections = 100
password_encryption = on
port = 5432
shared_buffers = '24MB'
ssl = off
ssl_ciphers = 'ALL:!ADH:!LOW:!EXP:!MD5:@STRENGTH'
unix_socket_directories = '/var/run/postgresql'

we need to parse the following types:

• logging_collector = on
• log_directory = 'pg_log'

This PR adapts to the regular expression to allow:

describe postgres_conf('/etc/postgresql/9.4/main/postgresql.conf') do
    its('logging_collector') { should eq 'on' }
    its('log_directory') { should eq 'pg_log' }
  end

[arlimus]

Thank you @chris-rock , just one comment ;)

[arlimus]

i'd change [']* to [']?

[arlimus]

Is it possible to have an empty assignment? vv

a = 

[chris-rock]

Haven't seen an empty assignment, but we should enable this. I'll update the unit tests accordingly.

[arlimus]

lgtm 👍 +1