Add quote_char parameter to the ini_subsetting resource type

The quote_char is used to quote the entire setting when it is modified
as a result of changes to some subsettings.

For an example let's assume we have a setting of this form:
  JAVA_ARGS=-Xmx256m
and we want to add the '-Xms' parameter to the setting, for that purpose
we define a resource like this:
  ini_subsetting { '-Xms':
    ensure     => present,
    path       => '/some/config/file',
    section    => '',
    setting    => 'JAVA_ARGS',
    subsetting => '-Xms'
    value      => '256m',
  }
which results into the following setting:
  JAVA_ARGS=-Xmx256m -Xms256m
But this is not what we intended - if this setting is read by the bash
shell the '-Xms256m' parameter is interpreted as a command to be
executed rather than a value to be assigned to the JAVA_ARGS variable.

To fix this problem the quote_char parameter was added to the
ini_subsetting resource type, and we'll take advantage of it to fix the
problem in the above example like so:
  ini_subsetting { '-Xms':
    ensure     => present,
    path       => '/some/config/file',
    section    => '',
    setting    => 'JAVA_ARGS',
    quote_char => '"',
    subsetting => '-Xms'
    value      => '256m',
  }
which will result into:
  JAVA_ARGS="-Xmx256m -Xms256m"
which is what we intended.
Tests for the quote_char parameter.
Merge pull request #95 from mruzicka/feature/master/quote-char-parameter-for-subsetting

Add quote_char parameter to the ini_subsetting resource type