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:
```sh
JAVA_ARGS=-Xmx256m
```
and we want to add the ```-Xms``` parameter to the setting, for that purpose we define a resource like this:
```puppet
  ini_subsetting { '-Xms':
    ensure     => present,
    path       => '/some/config/file',
    section    => '',
    setting    => 'JAVA_ARGS',
    subsetting => '-Xms'
    value      => '256m',
  }
```
which results into the following setting:
```sh
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:
```puppet
  ini_subsetting { '-Xms':
    ensure     => present,
    path       => '/some/config/file',
    section    => '',
    setting    => 'JAVA_ARGS',
    quote_char => '"',
    subsetting => '-Xms'
    value      => '256m',
  }
```
which will result into:
```sh
JAVA_ARGS="-Xmx256m -Xms256m"
```
which is what we intended.